104 PHYSIOLOGICAL VIEWS. 



the seed may have been placed in the ground. A botanist once 

 planted in a pot, six acorns, with the points of their embryos up- 

 ward. At the end of two months, upon removing the earth, he 

 found that all the radicles had made" an angle, in order to reach 

 downward. It is supposed that if the root met with no obstruction 

 in going downward, it would always be perfectly straight. 



Fig. 114 is a representation of a germina- 

 ting seed of the Mirahilis, (four o'clock ;) it 

 will be seen that the radicle, a, has made 

 nearly a right angle in turning downward ; 

 the plume is not developed. 

 ^ If you put cotton into a tumbler of water, 

 Fig. 114. ^^^ and place upon it some seeds of rye or wheat, 



you will see all the fibres shooting from the 

 seeds, in a perpendicular direction, downward. It is a very simple 

 and 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, ex- 

 tends itself in the natural direction from which it proceeds ; while 

 some imagine that the plant is endowed with a kind of instinct, 

 similar to that which appears in animals from their first moments of 

 existence, leading the little duck to seek the water, and the young 

 bird to fly. Let us call this power by what name we will, or refer it 

 to whatever secondary laws, we must ultimate^ attribute it to the 

 will and design of Him who gave the plant its living principle. 



After the young root has made some progress, the cotyledons 

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

 seed-leaves. When the plume develops its leaves, these seed-leaves- 

 being no longer needed wither and decay. 



You will recollect that the embryo or germ is composed of two 

 principal parts, the radicle and plume. The radicle, we have just 

 seen, extends itself downward. Soon after this part of the germ 

 has begun its downward course, the plume, (so called from its re- 

 sembling a httle feather,) rises upwards, and soon becomes a tuft of 

 young leaves, with which the stem, if there be one, ascends. 



" Some rye being planted in a good soil, 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 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 belongs to that class of plants whose seeds have but one 

 cotyledon, an^d 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 nourishing the embryo during its 

 germination, as the cotyledons of dicotyledonous plants. In some 

 monocotyledons is perceived under the albumen, 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 cjrn. 



* Sumner. 



Describe the experiment with acorns.— Describe Fig. 114— Causes assigned for the 

 downward course of the radicle — Seed leaves- Plume — Experiment with rye — Seeds 

 with one cotyledon— Vit^jllus. 



