4 ROOT AND SHOOT 



the testa is occupied by the embryo. The embryo (fig. 2) has 

 a small rod-like main axis, which is composed of the primary or 

 main root, the radicle {r) ; the primary or main stem {pi) ; and 

 a part of the axis, the hypocotyl (hp), which connects the root and 

 stem. The tip of the young root lies close within the pore 

 of the testa. No lateral roots occur on the radicle at this stage. 

 The main body of the embryo is constituted of the two large 

 fleshy leaves — the cotyledons (cot), which are attached to that 



Fig. I. — Seed of Bean. 



Fig. 2. — Embryo of Bean, with 

 Cotyledons separated. 



portion of the axis which is termed the hypocotyl. Lying 

 hidden between the two cotyledons is the minute main stem, 

 which terminates in a small bud. Thus, beginning at the root, 

 the axis has no lateral members on its root-portion : above 

 succeeds the hypocotyl* with two lateral cotyledons : still 

 higher the axis represents the young main stem, and bears a 

 few lateral commencements of leaves. 



When the seed germinates, the various parts of the embryo 

 emerge. The radicle elongates and becomes the primary 

 root : it grows -downwards and produces lateral roots which 

 may branch in their turn. The little stem grows upwards 

 and sends out from its sides, leaves, branches, and flowers ; 

 its branches may in turn bear, not only leaves, but also 

 branches of their own. We thus see that the development 

 of this flowering plant from its embryo consists in the 

 elongation of its primary axis, and the production of lateral 

 members on that axis. The parts possessed by a mature 

 flowering plant, whether it be a large tree or a small herb, 

 are all to be traced back to the primary axis. 



* It is impossible to define exactly the limits of the hypocotyl unless 

 the compound microscope be employed. 



