88 



HISTORY OF THE VEGETABLE KINGDOM. 



agency of insects, is tliat of the aristolochia cle- 

 matitis. The corolla of this flower, which is 

 tubular, hut terminating upwards in a ligulate 

 limb, is inflated into a globular figure at the 

 base. The tubular part is internally beset with 

 stiff hairs pointing downwards. The globular 

 part contains the pistil, which consists merely 

 of a gennen and stigma together with the sur- 

 rounding stamens. But the stamens being 

 shorter than even the gemien, cannot discharge 

 the pollen so as to throw it upon the stigma, as 

 the flower stands always upright, till after im- 

 pregnation. And hence without some additional 

 and peculiar aid, the pollen must necessarily fall 

 down to the bottom of the flower. Now the 

 aid that nature has furnished in this case is that 

 of the agency of the tipula pennicornis, a small 

 insect, which, entering the tube of the corolla 

 in quest of honey, descends to the bottom and 

 rummages about till it becomes quite covered 

 with pollen ; but not being able to force its way 

 out again owing to the downwai-d position of 

 the hairs, which converge to a point like the 

 wires of a mouse-trap, and being somewhat im- 

 patient of its confinement, it brushes backwards 

 and forwards trying every comer, till after re- 

 peatedly traversing the stigma it covers it with 

 pollen sufficient for its impregnation ; in conse- 

 quence of which the flower soon begins to droop, 

 and the haiis to shrink to the side of the tube, 

 effecting an easy passage for the escape of the 

 insect. 



Monoecious plants are, according to Spregnel, 

 mostly impregnated by insects also, excepting 

 such as are destitute of nectaries. But many of 

 them do not require that aid, in which case the 

 male and female flowers stand close together, as 

 in typha, coix, carex; the females being lowest, 

 and their petals being deeply or minutely lacin- 

 iated so as not to interrupt the pollen in its fall, 

 as in the genus Pinus. 



The impregnation of dioecious plants is often 

 effected by insects also, as has been already seen 

 in the case of the fig, and their flowers are said 

 to be always furnished with nectaries ; the male 

 flowers being larger than the female flowers, that 

 the insect, as it has been thought, may have 

 the better opportunity of loading itself with 

 pollen. 



From the fact of the agency of insects in con- 

 veying the pollen to the stigma, it will follow 

 that no plant requiring such aid can possibly 

 perfect its seed unless the specific insect has ac- 

 cess to it, or unless some such aid is given to it 

 by the cultivator. And hence botanists attri- 

 bute the imperfection of the seeds of hot-house 

 plants to the want of the insect by which the 

 species may be impregnated in its native climate. 

 This conjecture is countenanced by the following 

 experiment, as related by Willdenow: — A plant 

 of ubroma migttata had flowered for many yeai's 



in a hot-ho<ise at Berlin without producing any 

 fruit ; but when the gardener, by means of a hair 

 pencil, placed a little of the pollen upon the 

 stigma of several of the flowers, perfect fi-uit 

 was produced, from which new plants were 

 raised. 



In dioecious plants, the palms, for example, 

 fecundation may be artificially effected, as we 

 have already stated. Linnseus even maintained 

 that, not only may a single flower of a plant be 

 artificially impregnated by this method, but 

 that even a single cell of a niultilocular ovary 

 may be fecundated, by placing the pollen in 

 contact with only one of the divisions of the 

 stigma. It has been proved, however, that al- 

 though the poOen should touch only one of the 

 lobes of a stigma, all the cells of the ovary are 

 equally fecundated. But in whatever manner 

 fecundation has been effected, it always announces 

 its influence by visible appearances. The flower, 

 which until then was fresh, and often adorned 

 with the most lively tints, soon loses its beautiful 

 colouring, and resigns its transient splendour. 

 The corolla fades, the petals wither and fall off. 

 The stamina, having performed the functions 

 for which nature had called them into existence, 

 share the same fate. In a short time the pistil 

 remains alone in the centre of the flower. The 

 stigma and style, now become useless, also dis- 

 appear. The ovary alone continues, it being in 

 it that nature has deposited, to be there brought 

 to maturity, the rudiments of future genera- 

 tions. 



The ovary, when developed, forms the fruit. 

 It is not uncommon to see the calyx remaining 

 and accompanying it, until it attains its full 

 maturity. It is to be remarked, that this takes 

 place chiefly when the calyx is monosepalous. 

 If the ovary is inferior or parietal, the calyx 

 is then necessarily persistent, as it is intimately 

 united to the ovary. 



In the winter-cherry (physalis aliekngi,) the 

 calyx remains after fecundation, becomes red, 

 and forms a vesicular shell, in which the fruit 

 is contained. In the narcissus, the apple, the 

 pear, in short, in all plants which have the ovary 

 inferior or parietal, the persistent calyx fonns 

 the outer wall of the fruit. 



Shortly after fecundation has taken place, the 

 ovary begins to enlarge. The ovules which it 

 contains, and which are at first of a watery, and 

 in some degree inorganic substance, gradually 

 acquire consistence. The part which is to con- 

 stitute the perfect seed, in other words, the em- 

 bryo, gradually assumes development. All its 

 organs acquire a decided form, and, in a short 

 time, the ovary possesses the characters neces- 

 sary to constitute a fruit. 



We here conclude what relates to the flower 

 properly so called, considered in a general point 

 of view, and with reference to its constituent 



J 



