Book I. 



SEXUALITY OF VEGETABLES. 



181 



lettuce smooth, and the acrid celery wholesome. Pot-herbs are also rendered more tender 

 by means of cultivation, and better fitted for the use of man ; and so also are all our fine 

 varieties of fruit. 



810. Duration. Plants are either annuals, biennials, or perennials, and the species is 

 uniformly of the same class. But it has been found that some plants which are annuals 

 in a cold climate, such as that of Sweden, will become perennials in a hot climate, such 

 as that of the West Indies ; this anomaly has been exemplified in tropaeolum, beet-root, 

 and malva arborca : and, on the contrary, some plants, which are perennials in hot climates, 

 are reduced to annuals when transplanted into a cold climate ; this has been exemplified 

 in ricinus. 



Sect. VI. Of the Sexuality of Vegetables. 



811. The doctrine that plants are of different sexes, and winch constitutes the found- 

 ation of the Linnean system, though but lately established upon the basis of logical in- 

 duction, is by no means a novel doctrine. It appears to have been entertained even 

 among the original Greeks, from the antiquity of their mode of cultivating figs and palms. 

 Aristotle and Theophrastus maintain the doctrine of the sexuality of vegetables; and 

 Pliny; Dioscorides, and Galen, adopted the division by which plants were then distributed 

 into male and female ; but chiefly upon the erroneous principle of habit or aspect, and 

 without any reference to a distinction absolutely sexual. Pliny seems to admit the dis- 

 tinction of sex in all plants whatever, and quotes the case of the palm-tree as exhibiting 

 the most striking example. 



812. Discoveries of the moderns. Ca?salpinus, in the sixteenth century, denominates trees which pro- 

 duce ffuit only, females ; and trees of the same kind which are barren, males ; adding, that the fruit is 

 found to be more abundant and of a better quality where the males grow in the neighbourhood of the 

 females, which is, he says, occasioned by certain exhalations from the males dispersing themselves -all 

 over the females, and by an operation not to be explained, disposing them to produce more perfect seed. 

 About the middle of the seventeenth century, the doctrine of the sexes of the plants began to assume a 

 more fixed and determinate character. Malpighi describes the stamens, anthers, and pollen : the merit of 

 suggesting the use of the latter seems to be between Sir T. Millington, Savilian Professor at Oxford, and 

 the celebrated Dr. Grew. The "opinion of Grew was adopted also by Ray. The first example of experi- 

 ment recorded on this subject is that of Camerarius, professor of botany at Tubingen, who having 

 adopted the opinions of Grew and Raj-, though without perhaps regarding their arguments as the best that 

 could be adduced, conceived that the subject might be still further illustrated by means of depriving the 

 plant of its male flowers altogether, or of removing the individuals of a different sex to a distance from 

 one another. Accordingly having selected some plants of mercurialis, morus, zea mays, and ricinus, 

 and stripped them of their staminiferous flowers, or removed the male plant to a great distance from the 

 female, he found that the fruit did not now ripen ; the inference from which was, that the generation of 

 plants is analogous to that of animals, and that the stamens of the flowers of the former correspond to the 

 sexual organs of the males of the latter. The great and illustrious Linnaeus, reviewing with his usual 

 sagacity the evidence on which the doctrine rested, and perceiving that it was supported by a multiplicity 

 of the most incontrovertible facts, resolved to devote his labors peculiarly to the investigation of the 

 subject, and to prosecute his enquiries throughout the whole extent of the vegetable kingdom ; which great 

 and arduous enterprise he not only undertook but accomplished with a success equal to the unexampled 

 industry with which he pursued it. So that by collecting into one body all the evidence of former dis- 

 covery or experiment, and by adding much that was original of his own, he found himself at length 

 authorised to draw the important conclusion that no seed is perfected without the previous agency of 

 the pollen ; that the doctrine of the sexes of plants is consequently founded in fact. 



813. Proofs from the economy of the aquatics. Many 

 plants of this class that vegetate for the most part wholly 

 immersed in water, and often at a considerable depth, 

 gradually begin to elevate their stems as the season of* 

 flowering advances, when they at last rear their heads 

 above the surface of the water, and present their opening 

 blossoms to the sun, till the petals have begun to fade, 

 when they again gradually sink down to the bottom to 

 ripen and to sow their seeds. This very peculiar economy 

 may be exemplified in the case of ruppia maritima, and 

 several species of potamogeton, common in our ponds 

 and ditches ; from which we may fairly infer, that the 

 flowers rise thus to the surface merely to give the pollen 

 an opportunity of reaching the stigma uninjured. But 

 the most remarkable example of this kind is that of the 

 valisneria spiralis {fig. 63.), a plant that grows in the 

 ditches of Italy. The plant is of the class Dicecia, pro- 

 ducing its fertile flowers on the extremity of a long and 

 slender stalk twisted spirally like a corkscrew, which- 

 uncoiling of its own accord, "about the time of the open- 

 ing of the blossom, elevates the flowers to the surface of 

 the water, and leaves them to expand in the open air. 

 The barren flowers are produced in great numbers upon 

 short upright stalks issuing from a different root, from 

 which they detach themselves about the time of the 

 expansion of the female blossom, mounting up like little 

 air bubbles, and suddenly expanding when they reach the surface, where they float about in great 

 numbers among the female blossoms, and often cling to them in clusters so as to cover them entirely ; 

 thus bringing the stamens and pistils into immediate contact, and giving the anthers an opportunity of 

 discharging their pollen immediately over the stigma. When this operation has been performed, the now 

 uncoiled stalk of the female plant begins again to resume its original and spiral form, and gradually sinks 

 down, as it gradually rose, to ripen its fruit at the bottom of the water. We have gathered (in 1819) 

 these stalks, in the canals near Padua, upwards of ten feet long. 



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