610 COTYLEDONS. 



ill which it. fixes itself by numerous lateral fibres. The bud has meanwhile 

 grown out and formed a shoot which develops scale-leaves below, with gi-een 

 foliage-leaves above these, and so grows up to the surface of the water. The 

 exhausted cotyledon never leaves the interior of the nut, but gradually decays 

 with it. Thus we have here the rare instance of one cotyledon being extruded 

 from the cavity of the seed (that is to say, of the fruit) while the other remains 

 behind. 



In the seventh case the embryo exhibits two (only exceptionally more than 

 two) cotyledons, which are drawn out of the seed -coat during germination, 

 and spreading out in the sunlight, turn green and serve as foliage -leaves. 

 These foliage - leaves first function as absorbent organs ; that is to say, they 

 adjoin a special reserve-tissue in the seed from which they derive the materials 

 required for their first growth, and do not issue from the cavity of the seed 

 until the storehouse is exhausted and emptied of food. This is the case, for 

 example, in the repeatedly-mentioned Corn-cockle {Agrostemma Githago), whose 

 two cotyledons, folded together, are bent like a horse-shoe round the reserve- 

 tissue, but are withdrawn from the seed -coat after the consumption of this 

 food, when they separate and become green (c/. 141 ^' ^' *■ ■"•). Much more rai-ely 

 the seed-coat bursts at the beginning of germination, the large folded cotyledons 

 together with the surrounding reserve-tissue are drawn out so that the absoi-p- 

 tion of the reserve -food does not take place till after vacating the seed -coat, 

 after which follows the unfolding and colouring of the two cotyledons in the 

 sunlight. The seeds of Ricinus {cf. figs. 141 ^ and 141") show this process of 

 development, which on the whole is very uncommon. On the other hand, it 

 frequently happens that no special reserve -tissue (endosperm) is present, that 

 the small amount of reserve-food is deposited in the cotyledons themselves, and 

 that immediately after germination has commenced the two cotyledons leave 

 the cavity of the seed-coat and become green foliage-leaves. As an example of 

 this the germination of the Gourd (Cucurbita Pepo) is given in fig. 145 ^. 



The way in which cotyledons are withdrawn from the cavity of the seed-coat 

 is very characteristic, and it is worth while to inspect the most remarkable con- 

 trivances of this kind somewhat more carefully. One of the most peculiar is 

 observed in the seed and embryo of the Gourd, which is figured opposite in natural 

 size. The seed of the Gourd is pretty large, flattened, oval in outline, rounded at 

 one end, and somewhat tapering at the other, and here cut off" short, and pi'ovided 

 with a small aperture. If these seeds are disseminated they lie flat on the ground, 

 and easily glue themselves to the soil, especially if their surface is covered with the 

 adhesive juice of the fleshy fruit, as is always the case when the seeds are naturally 

 distributed. Since the embryo inclosed by the seed-coat is straight, it has a position 

 parallel to the surface of the ground. When germination begins the radicle is first 

 of all pressed out through the small opening mentioned. It immediately arches and 

 grows quickly downwards into the earth by the help of the food conveyed to it by 

 the two cotyledons. It there develops lateral rootlets, and unites firmly with the 



