72 



DEVELOPMENT OF FLOWERING OE PH^NOGAMOUS 



or, in other words, it is a primary stem crowned with a leaf-hud. 

 When it grows, this stem elongates throughout its whole length, so 

 as usually to raise the budding apex above the surface of the soil, 

 into the light and air, where its cotyledons expand into leaves ; and 



at the same time from the opposite ex- 

 tremity is formed the root, which grows 

 in a downward direction, so as to pen- 

 etrate more and more into the soil. The 

 two extremities of the embryo are dif- 

 ferently organized, are diflPerently affect- 

 ed by light and air, and grow in opposite 

 directions. The budding end invalua- 

 bly turns towards the light, and grows 

 upwards into the air ; the root-end turns 

 constantly from the light, and buries it- 

 self in the dark and moist soil. These 

 tendencies are absolute and irreversible. 

 If the budding end happen to lie point- 

 ing downwards and the root end up- 

 ""^ wards, both will curve quite round as 



they grow to assume their appropriate positions. If obstacles inter- 

 vene, the root will take as nearly a downward, and the stem as 

 nearly an upward direction, as possible. These are .only the first 

 manifestations of an inherent property, which continues, with only 

 incidental modifications, throughout the whole growth of the plant, 

 although, like instinct in the higher animals, it is strongest at the 

 commencement : and it insures that each part of the plant shall be 

 developed in the medium in which it is designed to live aryi act, — 

 the root in the earth, and the stem and leaves in the air. The 

 plantlet, therefore, possesses a kind of polarity; it is composed of 

 two counterpart systems, namely, a Descending Axis, or root, and an 

 Ascending Axis, or stem. The point of union or base of the two 

 has been termed the crown, neck, or collar. Both the root and stem 

 branch ; but the branches are repetitions of the axis from which 

 they spring, and obey its laws ; the branches of the root tending 

 to descend, and those of the stem to ascend. 



FIG. 106. A germinating embryo of Sugar-Maple, more advanced ; a, the radicle elongated 

 into tlie first joint of stem, bearing the unfolded cotyledons or seed-leaves, 6, and between 

 them the plumule (c), or rudiments of the next pair of leaves ; while from its lower extremity 

 the root, d, is formed. 



