(512 COTYLEDONS. 



The splitting of the seed-coat and the withdrawal of the cotyledons in the 

 Gourd are materially assisted by the development of a projecting lip at the union of 

 the radicle and hypocotyl. This lip presses against the lower edge of the hard seed- 

 coat, and holds it to the ground, so that after the bursting takes place the upper 

 portion of the seed-coat is raised up lid- wise from the lower. A smaller projection 

 is also developed on the hypocotyl in the embryo of the Sensitive Plant (Mimosa 

 pudica), and in that of Cuphea, and here again it presses against the lower part of 

 the seed-husk, and so assists both the bursting and the withdrawal. When the 

 seeds are surrounded by a pericarp, sometimes bands and projecting corners 

 are developed on it, sometimes projecting edges of the dried calyx and the like, 

 which serve as a fulcrum to the lip of the hypocotyl. The presence of numerous 

 structures formerly considered to be stunted organs useless to the plant thus receives 

 its natural explanation. 



Many plants, e.g. certain Umbelliferse, develop a very short hypocotyl. This 

 does not bend, and exercises only an insignificant strain, or perhaps none at all, on 

 the cotyledons, and so would not be able to release them from the integument of 

 the seed or fruit-husk. In all these plants the cotyledons have long stalks, and 

 these assume the function of the hypocotyl, at least in so far as the withdrawal of 

 the blades of the cotyledons is caused by them in the same way. This phenomenon 

 is very noticeable in the germination of the Asafoetida (Scorodosma Asa foetida), as 

 is clearly shown in fig. 145 2 . The stalks of the cotyledons, arising from the very 

 short hypocotyl, rapidly elongate, and exhibit the same s-shaped bend as that 

 formed in the hypocotyl of the Gourd seedling. These stalks also produce a similar 

 effect on the blades of the cotyledons still lying within the fruit-husk, and actually 

 draw them out. As soon as this has happened, the stalks straighten, and the 

 blades borne by them turn their upper surfaces towards the light. 



Almost a third of all seed-bearing plants have cotyledons whose liberation from 

 the bondage of the seed-coat or pericarp is effected in this manner, and this 

 consequently is the form of cotyledons which has been most frequently observed 

 and described. Much less frequently the two cotyledons make their appearance at 

 one end of the pericarp or seed-coat, while the radicle grows out at the opposite 

 end. In this case, which must be regarded as the eighth of the series here given, 

 the embryo is straight, and the hypocotyl is short and bears two thick cotyledons 

 whose apices, lying close together, form a truncated cone. When the radicle has 

 been once pushed out, and has planted itself firmly in the ground, the hypocotyl 

 at once elongates in the opposite direction without bending, pushes the folded 

 cotyledons in front of it, and presses them out of the fruit-husk. The tissue of the 

 fruit-husk lying above the cotyledonary cone must be pierced, and this is not 

 difficult to do, since this tissue consists of thin- walled cells. When the radicle has 

 grown out from one pole, and the pair of cotyledons from the other, the seedling 

 is surrounded half-way up by the vacated fruit -husk, as though by a girdle 

 (cf. fig. 145 5 ). The apices of the cotyledons still folded cone-like together 

 usually bore through the soil above the husk after they have left the cavity, and 



