THE FRUIT AND ITS ENVELOPES. 



97 



posite seams, to which the seeds are alternately 

 attached. It is said to be siliculous, if the trans- 

 verse and longitudinal diameters are equal or 

 nearly so, as in thlaspi, fig. a ; and siliquose, if the 

 longitudinal diameter exceeds the transverse, so 

 as to give to the pod the oblong figure, as in 

 cfieiranthuSjSig. b. In brassica the pod is cylindri- 

 cal, in crysiumum it is four cornered, in Upidium it 

 is elliptical, and in thlaspi it is inversely heart- 

 shaped. The surface of the pod is generally 

 smootli or pubescent, but in raphanus and sin- 

 apis, it is covered with protuberances. Though 

 the valves are generally two, yet the pod of the 

 genus bunias is wholly without valves. In 

 dentaria the valves open with a sudden jerk, 

 and in cardamin, after opening, they roll back 

 spirally. Sometimes the partitions are parallel 

 to the valves, as in draha, and sometimes they 

 are contrary, as in suhdarica, but always longi- 

 tudinal. The cells of the silique are generally 

 two in number, as in cheii-anthus, but some- 

 times the valves are w-ithout partitions, and 

 the pods consequently are celled, as in the genus 

 isatis. 



The legume is a dry and 

 elongated pericarp, con- 

 sisting of two valves with 

 two opposite seams, to the 

 one of which only the 

 seeds are attached, as ex- 

 emplified in the pea and 

 bean. It consists, for the 

 most part, of one cell only, 

 as in cathyrus; but some- 

 times it consists of two 

 ceUs as in astragalus, and Pci. 



sometimes of many, as in lotus. It is one seeded, 

 as in trifnlium procumiens; two seeded, as in 

 trifoli'u/mfragiferwm; or many seeded, as 'uipisum. 

 Its figure is oblong, as in ulex; or cylindrical, as 

 in orobiis; or compressed, as in hippocrassi; or 

 rhomboidal,as in ononis; orgibbous,as in astrag- 

 alus; or spiral, as in medicago; or inversely heart- 

 shaped, as in polygala. The substance of the 

 legume, when ripe, is membranaceous, as in med- 

 icago; or leathery, as in vicia ; orfirm and woody, 

 as in mimosa; sometimes the surface is smooth, 

 at others rough. Such is the general charac- 

 ter of the legume ; but there is also a peculiar 

 variety of it, which, though externally forming 

 longitudinal sutures, to one of which only the 

 seeds are attached, does not yet open longitud- 

 inally by means of two general valves, but trans- 

 versely, by means of joints; each joint fomiinga 

 cell that contains one seed, which is finally ex- 

 tricated by the opening of the individual joint 

 when detached. This variety of the legume is 

 regarded by Wildenow as constituting a dis- 

 tinct species of pericarp, designated by the name 

 of commentum. But it is a distinction to which 

 it seems scarcely entitled. 



64. 



Tlio strobile or cane is a 

 hard and woody pericarp, 

 consisting of the general 

 receptacle and indurated 

 scales of the catkin; in 

 some cases, however, as in 

 the larch, the scales are 

 rather leathery than woody, 

 and in others, as the com- 

 mon fir, {pinus ^hestris,) 

 they are beset with tuber- 

 Fir cone. cles. Under each scale 

 there is lodged one or more seeds or nuts, ir. 

 which the seeds are contained. The figure ot 

 the strobile is generally conical, or cylindrical, 

 as in most species of pines, but sometimes also it 

 is spherical, as in the cedar. In the mature state 

 of the fruit, the scales which are now closely 

 imbricated, cover the seeds or nuts so completely 

 as to assume the appearance of forming only one 

 compact whole, and thus the strobile hangs upon 

 the tree during the whole of the winter season, 

 protecting the inclosed seeds, but the heats of 

 the succeeding summer have no sooner arrived, 

 than the scales, formerly close and compact, be- 

 gin to shrink and separate, detacliing themselves 

 from one another by the whole of their con- 

 nected surface, and thus forming a passage for 

 the discharge of the seeds. 



When a fruit has attained its full maturity, it 

 opens, the different parts of which it is composed 

 separate, and the seeds which it contains burst 

 the bands that, until now, kept them confined 

 in the cavity in which they were developed. 

 This action, by which the seeds are naturally 

 dispersed over the surface of the ground, at the 

 period when they are ripe, is called dissemina^ 

 tion. 



In the wild or natural state of plants, the 

 dissemination of the seeds is the most powerful 

 agent in the reproduction of species. In fact, 

 were the seeds contained in a fruit not to issue 

 in order to be dispersed over the earth and there 

 be developed, species would cease to be repro- 

 duced, and entire races would disappear; and, 

 as all plants have a detei-minate duration, a period 

 would necessarily arrive when all would have 

 ceased to live, and when vegetation would have 

 for ever disappeared fi:om the surface of the 

 globe. The commencement of dissemination 

 indicates the termination of life in annual plants, 

 for, before it can take place, it is necessary that 

 the fruit should have attained maturity, and 

 that it should have become in some degree dried, 

 but still this phenomenon does not take place, in 

 annual herbaceous plants, until the period when 

 vegetation has entirely ceased. In woody plants, 

 dissemination always takes place during the 

 period of rest into which they enter when their 

 liber has become exhausted, and is no longer able 

 to give rise to leaves or organs of fructification. 



N 



