Dissertations on the Sexes of Plants

Author: Carolus Linnaeus

Dissertations on the Sexes of Plants

Carl von Linne (Carolus Linnaeus)

Although the earliest observers of nature could not possibly be ignorant of the sexes of plants, it has been left for the philosophers of the present age to demonstrate them. And so abundant are the proofs of this phenomenon that not a single vegetable can be found which does not offer them to our consideration.

The Atabaians, from time immemorial, have derived their principal sustenance from the Phoenix, or Date-bearing Palm, the Persians from the Turpentine Tree, and the inhabitants of the Archipelago from the Fig, the people of Chios have likewise cultivated Mastich from the most remote ages. As it has all along been the practice of these nations to promote the action of the male trees on the female by the same means which they use at this day, they must certainly have been acquainted with the sexual difference in plants, upon which the success of this practice depends. It is altogether impossible that they should have been ignorant of a circumstance, which, in these trees at least is so apparent. If, however, we duly consider the fate of botanical science, we shall soon see why the doctrine in question has not been long ago universally understood and received.

The writings of the ancients show that botany had by no means made great progress among them, at the time when mathematics and astronomy had risen to a very high degree of perfection. The works of Theophrastus, Dioscorides, and Pliny, those repositories of ancient learning, have no pretensions to philosophy in this kind of study, notwithstanding the assiduity of Dioscorides in seeking out the uses of plants, and the industry of the writers on husbandry, especially among the Romans, in the advancement of agriculture. After the revival of literature, the first employment of botanists was to rescue from total destruction and oblivion the ruins of ancient erudition; but after some time, not finding their acquisitions pay for the labour spent in the search, they began to turn their attention to nature herself, and to describe plants from their observations, till they became so overwhelmed with the multitude of species, as almost to despair of finding the way in or out of their gardens; both the Indies daily furnishing them with so many novelties, that no memory was strong enough to retain them. At length systematic writers undertook to describe every plant according to its fructification, by this means to distinguish them from each other, and arrange them in a methodical manner; which undertaking has employed them to the present day. But as these very authors bestowed their chief attention upon the corolla and the fruit, the former because its beauty attracts the eye, and the latter because most remarkable for its use, it so happened that they did not take time to duly consider the minuter parts of the flower, till they found the larger quite insufficient to discriminate the immense numbers of vegetables, which were daily augmenting the catalogue of Flora. The later botanists have therefore been obliged to examine attentively everything that they were able to discover in the fructification, in order to find there certain and convenient marks of distinction. Among these parts, the stamina and pistilla, although generally very minute bodies, and on that account contemptuously neglected by former observers, were found so essential, that no flower could be discovered destitute of them. Hence these organs have ever since been reckoned of great moment, have obtained particular names, and their different parts have also been enumerated.

To say precisely who first discovered the sexes of plants, would be a work of the greatest difficulty, and of no kind of use. Many discoveries have proceeded gradually towards perfection, as rivers, although small and insignificant at their origin, by the addition of fresh streams in their course, become able at length to bear ships of the greatest burden. It cannot be denied, that the ancient cultivators of Palms, Figs, and Pistacia, were acquainted with this fact, at least in those trees, for they knew the necessity of suspending the male flowers over the female, in order to obtain fruit. Nor is it less certain, that the oldest writers have expressly mentioned the sexes of plants. But how little real knowledge of the matter they possessed, and on what slight grounds they held it, appears from their having frequently described plants as being severally male and female, which were not so. Nay, after the revival of literature, even in the last century, botanists retained so much of the ignorance of former times, that the most eminent teachers of the science, attempting to discriminate the sexes, very often called the female plant the male; which affords the most decisive proof of their ignorance that could possibly have been given.

Sir Thomas Millington, an Englishman, is handed down to us, by his countrymen, as the first discoverer of this doctrine, if he be entitled to the honor of a discovery, who left no information in writing of what he had observed. It is pretended that he was perfectly acquainted with the fact about the year 1676; and indeed, a very little while after him, Grew and Ray, both Englishmen, appear to have gone a good way in the discovery. Rud. Jac. Camerarius, and other authors, have explained a great number of particulars, but no one has done more than Vaillant, the great French botanist, who in an academical oration, published by Boerhaave, discovers an accurate knowledge of the fact, although he has not demonstrated it by arguments.

From that time, that is, from the year 1718, many have laboured to promote this opinion, especially the author of the Sexual System, who believes he has, in a number of different publications, clearly and decisively established the truth of it; although Pontedera has endeavored to refute him, and Alston has even, very lately, treated him with derision.

That the subject may be properly understood, it is in the first place necessary that we should accurately understand the nature of vegetable bodies.

The organs common in general to all plants are: 1st, The root, with its capillary vessels, extracting nourishment from the ground. 2nd. The leaves, which may be called the limbs, and which, like the feet and wings of animals, are organs of motion; for being themselves shaken by the external air, they shake and exercise the plant. 3rd. The trunk, containing the medullary substance, which is nourished by the bark, and for the most part multiplied into several compound plants. 4th. The fructification, which is the true body of the plant, set at liberty by a metamorphosis, and consists only of the organs of generation; it is often defended by a calyx, and furnished with petals, by means of which it in a manner flutters in the air.

Many flowers have no calyx, as several of the lily tribe, the Hippuris, etc., many want the corolla, as grasses, and the plants called apetalous; but there are none more destitute of stamina and pistilla, those important organs destined to the formation of fruit. We therefore infer from experience that the stamina are the male organs of generation, and the pistilla of the female; and as many flowers are furnished with both at once, it follows that such flowers are hermaphrodites. Nor is this so wonderful, as that there should be any plants in which the different sexes are distinct individuals; for plants being immovably fixed to one spot, cannot like animals, travel in search of a mate. There exists, however, in some plants a real difference of sex. From seeds of the same mother, some individuals shall be produced, whose flowers exhibit stamina without pistilla, and may therefore properly be called male; while the rest being furnished with pistilla without stamina are therefore denominated females; and so uniformly does this take place, that no vegetable was ever found to produce female flowers without flowers furnished with stamina being produced, either on the same individual or on another plant of the same species, and vice versa.

As all seed vessels are destined to produce seeds, so are the stamina to bear the pollen, or fecundating powder. All seeds contain within their membranes a certain medullary substance, which swells when dipped into warm water. All pollen, likewise, contains in its membrane an elastic substance, which, although very subtle, and almost invisible, by means of warm water often explodes with great vehemence. While plants are in flower, the pollen falls from their antherae, and is dispersed abroad, as seeds are dislodged from their situation when the fruit is ripe. At the same time that the pollen is scattered, the pistillum presents its stigma, which is then in its highest vigour, and, for a portion of the day at least, it moistened with a fine dew. The stamina either surround this stigma, or if the flowers are of the drooping kind, they are bent towards one side, so that the pollen can easily find access to the stigma, where it not only adheres by means of the dew of that part, but the moisture occasions its bursting, by which means its contents are discharged. That issued from it being mixed with the fluid of the stigma, is conveyed to the rudiments of the seed. Many evident instances of this present themselves to our notice; but I have nowhere seen it more manifest than in the Jacobean Lily (Amarylis formosissima), the pistillum of which, when sufficient heat is given the plant to make it flower in perfection, is bent downwards and from its stigma issues a drop of limpid fluid, so large that one would think it in danger of falling to the ground. It is, however, gradually re-absorbed into the style about three or four o’clock and becomes invisible until about ten the next morning, when it appears again; by noon it attains its largest dimensions; and in the afternoon, by a gentle and scarcely perceptible decrease it returns to its source. If we shake the antherae over the stigma, so that the pollen may [p.252] fall on this limpid drop, we see the fluid soon after become turbid and assume a yellow color; and we perceive little rivulets, or opaque streaks running from the stigma towards the rudiments of the seed. Some time afterwards, when the drop has totally disappeared, the pollen may be observed adhering to the stigma, but of an irregular figure, having lost its original form. No one, therefore, can assent to what Morland and others have asserted, that the pollen passes into the stigma, pervades the style and enters the tender rudiments of the seed, as Leeuwenhoeck supposed his worms to enter the ova. A most evident proof of the falsehood of this opinion may be obtained from any species of Mirabilis (Marvel of Peru), whose pollen is so very large that it almost exceeds the style itself in thickness, and, falling on the stigma, adheres firmly to it; that organ sucking and exhausting the pollen, as a cuttle fish devours everything that comes within its grasp. One evening in the month of August, I removed all the stamina from three flowers of the Mirabilis longiflora, at the same time destroying all the rest of the flowers which were expanded; I sprinkled these three flowers with the pollen of Mirabilis Jalappa; the seed-buds swelled, but did not ripen. Another evening I performed a similar experiment, only sprinkling the flowers with the pollen of the same species; all these flowers produced ripe seeds.

Some writers have believed that the stamina are parts of the fructification, which serve only to discharge an impure or excrementitious matter, and by no means formed for so important a work as generation. But it is very evident that these authors have not sufficiently examined the subject; for, as in many vegetables, some flowers are furnished with stamina only, and others only with pistilla; it is altogether impossible that stamina situated at so very great a distance from the fruit, as on a different branch, or perhaps on a separate plant, should serve to convey any impurities from the embryo.

No physiologist could demonstrate, a priori, the necessity of the masculine fluid to the rendering the eggs of animals prolific, but experience has established it beyond a doubt. We therefore judge a posteriori principally, of the same effect in plants.

In the month of January, 1760, the Antholyza Cunonia flowered in a pot in my parlour, but produced no fruit, the air of the room not being sufficiently agitated to waft the pollen to the stigma. One day, about noon, feeling the stigma very moist, I plucked off one of the antherae, by means of a fine pair of forceps, and gently rubbed it on one part of the expanded stigmata. The spike of flowers remained eight or ten days [p.253] longer; when I observed, in gathering the branch for my herbarium, that the fruit of that flower only on which the experiment had been made, had swelled to the size of a bean. I then dissected this fruit and discovered that one of the three cells contained seeds in considerable number, the other two being entirely withered.

In the month of April I sowed the seeds of hemp (Cannabis) in two different pots. The young plants came up so plentifully, that each pot contained thirty or forty. I placed each by the light of a window, but in different and remote apartments. The hemp grew extremely well in both pots. In one of them I permitted the male and female plants to remain together, to flower and bear fruit, which ripened in July, being macerated in water, and committed to the earth, sprung up in twelve days. From the other, however, I removed all the male plants, as soon as they were old enough for me to distinguish them from the females. The remaining females grew very well, and presented their long pistilla in great abundance, these flowers continuing a very long time, as if in expectation of their mates; while the plants in the other pot had already ripened their fruit, their pistilla having, quite in a different manner, faded as soon as the males had discharged all their pollen. It was truly a beautiful and truly admirable spectacle to see the unimpregnated females preserve their pistilla so long green and flourishing, not permitting them to begin to fade till they had been for a very considerable time exposed in vain, to the access of the male pollen.

Afterwards, when these virgin plants began to decay through age, I examined all their calyces in the presence of several botanists and found them large and flourishing, although every one of the seed-buds was brown, compressed, membranaceous, and dry, not exhibiting any appearance of cotyledons or pulp. Hence I am perfectly convinced that the circumstance which authors have recorded, of the female hemp having produced seeds, although deprived of the male, could only have happened by means of pollen brought by the wind from some distant place. No experiment can be more easily performed than the above; none more satisfactory in demonstrating the generation of plants.

The Clutia tenella was in like manner kept growing in my window during the months of June and July. The male plant was in one pot, the female in another. The latter abounded with fruit, not one of its flowers proving abortive. I removed the two pots into different windows of the same apartment; still all the female flowers continued to become fruitful. At length I took away the male entirely, leaving the [p.254] female alone, and cutting off all the flowers which it had already borne. Every day new ones appeared from the axila of every leaf; each remained eight or ten days, after which their foot stalks turning yellow, they fell barren to the ground. A botanical friend, who had amused himself with observing this phenomenon with me, persuaded me to bring, from the stove in the garden, a single male flower, which he placed over one of the female ones, then in perfection, tying a piece of red silk around its pistillum. The next day the male flower was taken away, and this single seed-bud remained, and bore fruit. Afterwards I took another male flower out of the same stove, and with a pair of slender forceps pinched off one of its antherae, which I afterwards gently scratched with a feather, so that a very small portion of its pollen was discharged upon one of the three stigmata of a female flower, the other two stigmata being covered with paper. This fruit likewise attained its due size, and on being cut transversely, exhibited one cell filled with a large seed, and the other two empty. The rest of the flowers, being unimpregnated, faded and fell off. This experiment may be performed with as little trouble as the former.

The Datifca cannabina came up in my garden from seed ten years ago, and has every year been plentifully increased by means of its perennial root. Flowers in great number have been produced by it; but, being all female, they proved abortive. Being desirous of producing male plants, I obtained more seeds from Paris. Some more plants were raised; but these likewise to my great mortification, all proved females, and bore flowers, but no fruit. In the year 1757 I received another parcel of seeds. From these I obtained a few male plants, which flowered in 1758. These were planted at a great distance from the females; and when their flowers were just ready to emit their pollen, holding a paper under them, I gently shook the spike of panicle with my finger, till the paper was almost covered with the yellow powder. I carried this to the females, which were flowering in another part of the garden, and placed it over them. The cold nights of the year in which this experiment was made, destroyed these Datifcas, with many other plants, much earlier than usual. Nevertheless, when I examined the flowers of those plants, which I had sprinkled with the fertilizing powder, I found the seeds of their due magnitude; while in the more remote Datifcas, which had not been impregnated with pollen, no traces of seeds were visible.

Several species of Momordica, cultivated by us, like other Indian vegetables, in close stoves, have frequently borne female flowers; which, although at first very vigorous, after a short time have constantly faded and turned yellow, without perfecting any seed, till I instructed the gardener, as soon as he observed a female flower, to gather a male one, and place it above the female. By this contrivance we are so certain of obtaining fruit that we dare pledge ourselves to make any female flowers fertile that shall be fixed on.

The Jatropha urens has flowered every year in my hot-house; but the female flowers coming before the males, in a week’s time dropped their petals and faded before the latter were opened; from which cause no fruit has been produced, but the germina themselves have fallen off. We have therefore never had any fruit of the Jatropha till the year 1752, when the male flowers were in vigour on a tall tree, at the same time that the females began to appear on a small Jatropha which was growing in a garden-pot. I placed this pot under the other tree, by which means the female flowers bore seeds, which grew in being sown. I have frequently amused myself with taking the male flowers from one plant, and scattering them over the female flowers of another, and have always found the seeds of the latter impregnated by it.

Two years ago I placed a piece of paper under some of these male flowers and afterwards folded up the pollen which had fallen upon it, preserving it so folded up, if I remember right, four or six weeks, at the end of which time another branch of the same Jatropha was in flower. I then took the pollen, which I had so long preserved in paper, and strewed it over three female flowers, the only ones at that time expanded. These three females proved fruitful, while all the rest, which grew in the same bunch, fell off abortive.

The interior petals of the Ornithogalum, commonly but improperly called Canadense, cohere so closely together that they only just admit the air to the germen and will scarcely permit the pollen of another flower to pass; this plant produced every day new flowers and fruit, the fructification never failing in any instance; I therefore, with the utmost care, extracted the antherae from one of the flowers with a hooked needle, and as I hoped, this single flower proved barren. This experiment was repeated about a week after with the same success.

I removed all of the antherae out of a flower of Chelidonium corniculatum (scarlet-horned poppy), which was growing in a remote part of the garden, upon the first opening of its petals, and stripped off all the rest of the flowers; another day I treated another flower of the same plant in a similar manner, but sprinkled the pistillum of this with the [p.256] pollen borrowed from another plant of the same species; the result was, that the first flower produced no fruit, but the second afforded very perfect seed. My design in this experiment was to prove that the mere removal of the antherae from a flower is not in itself sufficient to render the germen abortive.

Having the Nicotiana fruticosa growing in a garden-pot, and producing plenty of flowers and seed, I extracted the antherae from the newly expanded flowers before they had burst, at the same time cutting away all the other flowers; this germen produced no fruit, nor did it even swell.

I removed an urn, in which the Asphodelus fistulosus was growing, to one corner of the garden, and from one of the flowers which had lately opened, I extracted its antherae; this caused the impregnation to fail. Another day I treated another flower in the same manner; but, bringing a flower from a plant in a different part of the garden, with which I sprinkled the pistillum of the mutilated one, its germen became by that means fruitful.

Ixia chinensis, flowering in my stove, the windows of which were shut, all its flowers proved abortive. I therefore took one of its antherae in a pair of pincers, and with them sprinkled the stigmata of two flowers, and the next day one stigma only of a third flower; the seed-buds of these flowers remained, grew to a large size and bore seed, the fruit of the third, however, contained ripe seed only in one of its cells.

To relate more experiments would only be to fatigue the reader unnecessarily. All nature proclaims the truth I have endeavored to inculcate, and every flower bears witness to it. Any person may make the experiment for himself with any plant he pleases, only taking care to place the pot in which it is growing, in the window of a room sufficiently out of reach of other flowers; and I will venture to promise him that he will obtain no perfect fruit unless pollen has access to the pistillum.

Logan’s experiments on the Mays are perfectly satisfactory, and manifestly show that the pollen does not enter the style, or arrive at the germen, but that it is exhausted by the genital fluid of the pistillum. And as in animals no conception can take place, unless the genital fluid of the female be discharged at the same moment as the impregnating liquor of the male; so in plants, generation fails, unless the stigma be moist with prolific dew.

Husbandmen know, by long experience, that if rain fills while rye is in flower, by coagulating the pollen of its antherae, it occasions the emptiness of many husks in the ear.

Gardeners remark the same thing every year in fruit trees. Their blossoms produce no fruit if they have unfortunately been exposed to long-continued rains.

Aquatic plants rise above the water at the time of flowering, and afterwards again subside, for no other reason, than that the pollen may safely reach the stigma.

The white water-lily (Nymphaea alba) raises itself every morning out of the water and opens its flowers, so that by noon at least three inches of its flower-stalk may be seen above the surface. In the evening it is closely shut up, and withdrawn again; for about four o’clock in the afternoon the flower closes, and remains all night under water; which was observed full two thousand years since, even as long ago as the time of Theophrastus, who has described this circumstance in the Nymphaea Lotus, a plant so much resembling our white water-lily that they are only distinguished from each other by the leaves of the Lotus being indented. Theophrastus gives the following account of this vegetable, in his History of Plants, book IV., chap. 10: "It is said to withdraw its flowers into the Euphrates, which continue to descend till midnight, to so great a depth that at daybreak they are out of reach of the hand; after which it rises again, and in the course of the morning appears above the water, and expands its flowers, rising higher and higher, till it is a considerable height above the surface." The very same thing may be observed in the Nymphaea alba.

Many flowers close themselves in the evening and before rain, lest the pollen should be coagulated; but after the discharge of the pollen they always remain open. Such of them as do not shut up, incline their flowers downward in those circumstances, and several flowers, which come forth in the moisture of spring, droop perpetually. The manner in which the Parnassia and Saxigrage move their antherae to the stigma is well known. The common Rue, a plant everywhere to be met with, moves one of its antherae every day to the stigma, till all of them in their turns have deposited their pollen there.

The Neapolitan star flower (ornithogalum nutans) has six broad stamina, which stand close together in the form of a bell, the three external ones being but half the length of the others; so that it seems impossible for their antherae ever to convey their pollen to the stigma; out nature, by an admirable contrivance, bends the summits of these [p.258] external stamina inwards between the other filaments, so that they are enabled to accomplish their purpose.

The Plaintain tree (Musa) bears two kinds of hermaphrodite flowers; some have imperfect antherae, others only the rudiments of stigmats; as the last mentioned kind appear after the others, they cannot impregnate them, consequently no seeds are produced in our gardens, and scarcely ever on the plants cultivated in India. An event happened this year, which I have long wished for; two plaintain-trees flowering with me so fortunately that one of them brought forth its first female blossoms at the time that male ones began to appear on the other. I eagerly ran to collect antherae from the first plant, in order to scatter them over the newly-expanded females, in hopes of obtaining seed from them, which no botanist has yet been able to do. But when I came to examine the antherae I found even the largest of them absolutely empty and void of pollen, consequently unfit for impregnating the females; the seeds of this plant, therefore, can never be perfected in our gardens. I do not doubt, however, that real male plants of this species may be found in its native country, bearing flowers without fruit, which the gardeners have neglected; while the females in this country produce imperfect fruit, without seeds, like the female fig; and, like that tree, are increased easily by suckers. The fruit, therefore, of the plaintain-tree scarcely attains anything like its due size, the larger seed-buds only ripening, without containing anything in them.

The day would sooner fail me than examples. A female date-bearing palm flowered many years at Berlin, without producing any seeds. But the Berlin people taking care to have some of the blossoms of the male tree, which was then flowering at Leipsic, sent them by the post, they obtained fruit by that means; and some dates, the offspring of this impregnation, being planted in my garden, sprung up, and to this day continue to grow vigorously. Koempfer formerly told us how necessary it was found by the oriental people, who live upon the produce of palm-trees, and are the true Lotophagi, to plant some male trees among the females, if they hoped for any fruit; hence, it is the practice of those who make war in that part of the world to cut down all the male palms, that a famine may afflict their proprietors; sometimes even the inhabitants themselves destroy the male trees, when they dread an invasion, that their enemies may find no sustenance in the country.

Leaving these instances, and innumerable others, which are so well known to botanists that they would by no means bear the appearance of novelty, and can only be doubted by those persons who neither have observed nature, nor will they take the trouble to study her, I pass to a fresh subject, concerning which much new light is wanted; I mean hybrid, or mule vegetables, the existence and origin of which we shall now consider. I shall enumerate three or four real mule plants, to whose origin I have been an eye-witness.

1. Veronica spuria, described in Amoenitates Acad. vol. III. p. 35, came from the impregnation of Veronic maratima by Verbena officinalis; it is easily propagated by cuttings, and agrees perfectly with its mother in fructification, and with its father in leaves.

2. Delphinium hybridum, sprung up in a part of the garden where Delphinium clatum and Aconitum Napellus grew together; it resembles its mother as much in its internal parts, that is, in fructification as it does its father (the Aconitum) in outward structure, or leaves; and, owing its origin to plants so nearly allied to each other, it propagates itself by seed; some of which I now send with this Dissertation.

3. Hieracium Taraxici, gathered in 1753 upon our mountains by Dr. Solander, in its thick, brown, woolly calyx; in its stem being hairy towards the top, and in its bracteae, as well as in every parts of its fructification, resembles so perfectly its mother, Hieracium alpinum, that an inexperienced person might mistake one for the other; but in the smoothness of its leaves, in their indentations and whole structure, it so manifestly agrees with its father, Leontodon Taraxacum (Dandelion), that there can be no doubt of its origin.

4. Tragopogon hybridum attracted my notice the autumn before last, in a part of the garden where I had planted Tragopogon pratense, and Tragopogon porrifolium; but winter coming on, destroyed its seeds. Last year, while the Tragopogon pratense was in flower I rubbed off its pollen early in the morning, and about eight o’clock sprinkled its stigmata with some pollen of the Tragopogon porrifolium, marking the calyces by tying a thread round them. I afterwards gathered the seeds when ripe, and sowed them that autumn in another place; they grew, and produced this year, 1759, purple flowers yellow at the base, seeds of which I now send. I doubt whether any experiment demonstrates the generation of plants more certainly than this.

There can be no doubt that these are all new species produced by hybrid generation. And hence we learn, that a mule offspring is the exact image of its mother in its medullary substance, internal nature, or fructification, but resembles its father in leaves. This is a foundation upon which naturalists may build much. For it seems probable that many plants, which now appear different species of the same genus, may in the beginning have been but one plant, having arisen merely from hybrid generation. Many of those Geraniums which grow at the Cape of Good Hope, and have never been found wild anywhere but in the south parts of Africa, and which, as they are distinguished from all other Geraniums by their single-leaved calyx, many-flowered foot-stalk, irregular corolla, seven fertile stamina, and three mutilated ones, and by their naked seeds furnished with downy awns; so they agree together in all these characters, although very various in their roots, stems and leaves; these Geraniums, I say, would almost induce a botanist to believe that the species of one genus in vegetables are only so many different plants as there have been different associations with the flowers of one species, and consequently a genus is nothing else than a number of plants sprung from the same mother by different fathers. But whether all these species be the offspring of time; whether, in the beginning of all things, the Creator limited the number of future species, I dare not presume to determine. I am, however, convinced this mode of multiplying plants does not interfere with the system or general scheme of nature; as I daily observe that insects, which live upon one species of a particular genus, are contented with another of the same genus.

A person who has once seen the Achyranthes aspera, and remarked its spike, the parts of its flower, its small and peculiarly formed nectaria, as well as its calyces bent backwards as the fruit ripens, would think it very easy at any time to distinguish these flowers from all others in the universe; but when he finds the flowers of Achyranthes indica agreeing with them even in their minutest parts, and at the same time observes the large, thick, obtuse, undulated leaves of the last-mentioned plant, he will think he sees Achyranthes aspera masked in the foliage of Xanthium strumarium. But I forbear to mention any more instances.

Here is a new employment for botanists, to attempt the production of new species of vegetables by scattering the pollen of various plants over various widowed females. And if these remarks should meet with a favourable reception, I shall be the more induced to dedicate what remains of my life to such experiments, which recommend themselves by being at the same time agreeable and useful. I am persuaded by many considerations that those numerous and most valuable varieties of plants which are used for culinary purposes, have been produced in this manner, as the several kinds of cabbages, lettuces, etc.; and I apprehend this is the reason of their not being changed by a difference of soil. Hence I cannot give my assent to the opinion of those who imagine all varieties to have been occasioned by change of soil; for, if this were the case, the plants would return to their original form, if removed again to their original situation.

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Chicago: Carolus Linnaeus, Dissertations on the Sexes of Plants in The Library of Original Sources, ed. Oliver J. Thatcher (Milwaukee, WI: University Research Extension Co., 1907), 248–260. Original Sources, accessed February 24, 2020, http://www.originalsources.com/Document.aspx?DocID=4L2KU2GSVFLP39T.

MLA: Linnaeus, Carolus. Dissertations on the Sexes of Plants, in The Library of Original Sources, edited by Oliver J. Thatcher, Vol. 6, Milwaukee, WI, University Research Extension Co., 1907, pp. 248–260. Original Sources. 24 Feb. 2020. www.originalsources.com/Document.aspx?DocID=4L2KU2GSVFLP39T.

Harvard: Linnaeus, C, Dissertations on the Sexes of Plants. cited in 1907, The Library of Original Sources, ed. , University Research Extension Co., Milwaukee, WI, pp.248–260. Original Sources, retrieved 24 February 2020, from http://www.originalsources.com/Document.aspx?DocID=4L2KU2GSVFLP39T.