78 



THE GENERAL MORPHOLOGY OF THE PLANT. 



with a Bud. In germination the axis or radicle elongates through- 

 out, so as usually to elevate the budding apex above the surface of 

 the soil, and its cotyledons expand in the air into the first pair of 

 leaves ; and at the same time from the opposite extremity 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 therefore differently affected by the same external in- 

 fluences, by light especially, and exhibit exactly opposite tenden- 

 cies. The budding end invariably rises upwards, as if it sought 

 the light and air ; the root-end turns constantly from the light, and 

 buries itself in the dark and moist soil. These tendencies are ab- 

 solute and irreversible. If obstacles intervene, the root will take as 

 nearly a downward, and the stem as nearly an upward, direction as 

 possible. They are only the first manifestation of an inherent prop- 

 erty which continues, with only incidental modifications, through- 

 out 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 and act, the root in the earth, and the 

 stem and leaves in the air. The axis, therefore, especially in 



plants of the highest grade, possesses a kind of polarity ; it is com- 

 posed of two counterpart systems, namely, a Descending Axis or 



FIG. 99. A longitudinal section of a seed, showing the embryo or rudimentary plant it con- 

 tains. 100. The embryo taken from the seed, and its rudimentary leaves, or cotyledons, a 

 little separated. 101. The same in germination, the cotyledons expanding into the first pair of 

 leaves. 102-104. The seedling plant more advanced. (The radicle, or first joint of stem, 

 should have been drawn more elongated.) 



