154, ELEMENTS OF STEUCTUEAL BOTANY. 



expand and become the earliest leaves of the new plant ; 

 and during this upward extension of the radicle a toot 

 also is being rapidly developed from its lower end. It is 

 important, also, to notice here that the mode of growth of 

 the root portion is at variance with that of the radicle or 

 stem proper, for while the latter grows throughout its 

 length, the former grows by the addition of successive new 

 portions to its extremity. (The protection of the growing 

 root by a root-cap has already been referred to.) As soon 

 as the root is prepared to absorb nourishment from the 

 soil, then, and not till then, the development of the next 

 bit of stem commences between the first pair of leaves. 



255. But when the cotyledons are loaded with nour- 

 ishment, as in the Bean, it will generally be found that 

 the elements of additional bits of stem (the plumule) are 

 already present in the embryo, and although the radicle 

 may lengthen so as to lift the cotyledons above the 

 surface, yet these do not, as in the thin-leaved embryos, 

 fully perform the office of foliage-leaves ; their true 

 function is to supply the newly developing parts with 

 nourishment, and when this duty is performed they 

 usuallj* drop off. In fact, it is not uncommon for such 

 extremely fleshy cotyledons to remain under the surface 

 altogether, as in the case of the Pea and the Acorn. In 

 these cases the growth of the radicle is but slight. The 

 plumule and the end of the radicle are liberated from 

 the seed, and the former at once grows vigorously upwavd, 

 being practically independent of the root as long as one 

 stock of nourishment in the cotyledons holds uut. 

 Simultaneously with the development of the stem, the root 

 is \trongly developed from the end of the short radicie. 



