80 THE ROOT. 



what is really essential to vegetation. But the general scheme of 

 the vegetable kingdom, and the unity of plan which runs through 

 the manifold diversities it displays, enabling us to refer an almost 

 infinite variety of details to a few general laws, must be studied in 

 the higher series of Phsenogamous plants, which exhibit, in mani- 

 fold variety of form, the completed type of vegatation. 



CHAPTER III. 



OF THE ROOT OR DESCENDING AXIS. 



117. THE Organs of Vegetation (114) in Phsenogamous plants, 

 namely, the root, stem, and leaves, are to be considered in succes- 

 sion ; and it is on some accounts most convenient to begin with 

 the root, charged as it is with the earliest office in the nutrition of 

 the vegetable, that of absorbing its food. According to our view 

 of the matter, however (113), its formation does not precede, but 

 follows, that of the stem. 



118. The Primary Root, as already defined (112-114), is the de- 

 scending axis, or that portion of the trunk which, avoiding the 

 light, grows downwards, fixing the plant to the soil, and absorbing 

 nourishment from it. The examination of any ordinary embryo 

 during germination, such as that of the Sugar Maple (Fig. 105 - 

 107), will give a good idea of the formation and entire peculiarities 



of the root. Its radicle (), 

 or preexisting axis, first of all 

 grows in such a way as to elon- 

 gate throughout its whole ex- 

 tent (thus showing that it is not 

 itself root, but the first joint of 

 stem) ; this lengthening, while 



it thrusts the root-end downwards (113) a little deeper into the soil, 

 at the same time raises the cotyledons (b) to the surface, and at 

 length elevates them above it, where they expand in the light and 

 air, and begin to perform the office of leaves (Fig. 107). Contem- 



FIG. 105. An embryo of Sugar Maple, just unfolding in germination. 106. Same, a little 

 more advanced ; the radicle, a, considerably elongated. 



