136 PHYSIOLOGICAL VIEWS. 



interesting experiment. Some ascribe this phenomenon to the 

 laws of gravitation, by which the root is attracted towards the 

 centre of the earth ; others say that the radicle, stimulated by 

 moisture, extends itself in the natural direction from which the 

 moisture proceeds ; and some imagine that the plant is endow- 

 ed with a kind of instinct, similar to that which often appears 

 in animals from their first moments of existence, leading the 

 little duck to seek the water and birds to attempt to fly ; but 

 let us call this power by what name we will, or refer it to 

 whatever secondary laws, we must after all attribute it to the 

 will and design of Him, who gave the plant a principle of vi- 

 tality. 



After the young root has made some progress, the cotyle- 

 dons swell, and rising out of the ground form two green leaves, 

 called seed leaves. You have no doubt noticed their appear- 

 ance in the garden bean, when it first appears above the ground. 

 When the plume developes leaves, these seed leaves, being no 

 longer needed, they 'wither and decay. 



You will recollect that the embryo or germ is composed of 

 two parts, the radicle and the plume. The radicle, we have 

 just seen, extends itself downwards. Soon after this part of 

 the germ has begun its downward course, the plume, (so called 

 from its resembling a little feather,) rises upwards, and soon 

 becomes a tuft of young leaves, with which the stem, if there 

 is one, ascends. 



" Some rye," says a botanist, " was planted in a good soil, 

 and at the end of the second day its radicle was discernible. 

 At the end of twenty-four hours the embryo had escaped from 

 its integument. On the second day the fibres of the root had 

 augmented, but the leaves had not appeared. On the fourth 

 day the first leaf began to 4 appear above the ground, at which 

 time the colour was red. On the fifth day, it had grown to the 

 length of an inch, and its colour was now green, and on the 

 sixth day the second leaf had appeared." 



Rye, however, belongs to that class of plants whose seeds 

 have but one cotyledon ; this never rises above the ground to 

 form a seed leaf. Seeds with but one cotyledon are chiefly 

 composed of albumen, which performs the same office of nour- 

 ishing the embryo during its germination, as do the cotyledons 

 of dicotyledonous plants. In some monocotyledons is perceived 

 under the albumen or white, a part called Vitellus, or the yolk ; 

 this, like the albumen, is entirely converted into nourishment 

 for the young plant ; it may be seen in the seeds of grasses, 

 and is conspicuous in the Indian corn. 



Causes assigned for the downward course of the radicle Seed leaves 

 I lume Experiment with rye- Seeds with one cotyledon Vitellus. 



