COTYLEDONS. 60[> 



by their adjacent surfaces, as, for example, in the Chestnut, Horse -cliestnut, 

 and Nasturtiums. Everything which one is generally accustomed to consider 

 an attribute of a leaf is entirely wanting. When these seeds take up water 

 from the environment and begin to germinate and grow, first of all the seed- 

 coat bursts at one end of the seed, and the radicle together with the axis and 

 also the thick stalks of the two cotyledons are extruded through the rupture. 

 The cotyledons themselves, however, remain inside, lose weight in proportion as 

 they give up materials to the growing parts, dwindle, and finally appear quite 

 shrivelled and emptied. The extruded radicle has, on the contrary, visibly 

 increased, it bends downwards, penetrates vertically into the ground, and produces 

 lateral roots with root-hairs, which now absorb nourishment from the soil. The 

 bud which was hemmed in between the short thick stalks of the two cotyledons 

 has, on the other hand, curved upwards, elongated pretty quickly, and become 

 a shoot which in the Nasturtium immediately develops green, lobed foliage-leaves. 

 Tn other plants, e.g. in the Oak, first scale-leaves appear and then green foliage- 

 leaves above them. In fig. 144i'^'*''' these conditions are depicted both in the 

 Nasturtium and the Oak. The cotyledons have here a threefold part to play; 

 first of all they function as storehouses for reserve materials, and at the .same 

 time as protecting envelopes for the small squeezed rudiment of the future plant; 

 in addition they also have the task of thi'usting the embryo out of the cavity 

 of the seed so far that its members can elongate as required — some towards the 

 light, and some into the dark ground. When they have performed these duties 

 they die off" and disintegrate so completely that at the place where they were 

 connected with the h3'pocotyl, scarcely a trace of their insertion is to be recognized. 

 A peculiar condition of the cotyledons, the sixth in the series here described, 

 is observed in the Water Chestnut (Trapa). One of the cotyledons is small 

 and scale-like, containing no reserve materials ; the other is very large, and so 

 completely fills up the nut that it looks as if someone had poured wax into the 

 interior of the fruit, and that it had there become hardened into a solid mass. 

 The Water Che.stnut germinates on the mud under water. As soon as germina- 

 tion commences, a white worm-like body is extruded from the aperture of the 

 nut, and though many consider this to be the hypocotyl, it should, strictly 

 speaking, be regarded as a root (c/. fig. 144 ^). This structure elongates under 

 the water and grows directly upwards. Of the two cotyledons only that one 

 which was inserted as a tiny scale on the short hypocotyl, leaves the cavity 

 of the nut and is connected by a long stalk with the hypocotyl. This long 

 stalk, together with the very small hypocotyl and the root, pass so gradually 

 into one another that they resemble a single unjointed white cord (c/. fig. 144*). 

 The reserve materials deposited in the large, fleshy cotyledon are conducted by 

 the stalk-like connection to the growing parts of the embryo in the water; 

 a process which occupies a considerable time. By the time that this cotyledon 

 has yielded up the reserve food, the root has grown so strong that it is able 

 to take up materials from its surroundings ; it bends down towards the mud 



Vol. I. 39 



