18 PLAN OF VEGETATION. 



CHAPTER II. 



PLAI? OF VEGETATION. — ELEMENTARY ORGANS. 



18. The earliest and simplest state of the plant is an embryo 

 contained in a seed. Tliis consists essentially of t^vo parts, the 

 radicle and plumule ; the former about to be developed into the 

 root, the latter into the ascending plant with its appendages. 



19. As soon as the process of gerniuiation commences, the 

 radicle begins to extend itself downwards in the direction of the 

 earth's centre, constantly avoiding the ah and the light, forming 

 the descending axis, or root. The plumule, takmg the opposite 

 direction, extends itself upwards, always seeldng the light, and 

 expandmg itself, to the utmost extent of its power, to the mflu- 

 ence of the atmosphere. This constitutes the ascending axis, or 

 trunk, around wliich the leaves and their modifications are 

 arranged. 



20. At the commencement of its gro^vth, the ascendmg axis 

 is merely a bud, that is, a groiving point, enveloped m rudimen- 

 tary leaves, or scales, for its protection. As tliis growing point 

 advances, the enveloping scales expand into leaves below^, w^liile 

 new ones are constantly appearing, in succession, above. Thus 

 the axis is always terminated by a bud. 



21. By this process the axis is elongated, simply m one direc- 

 tion. But, besides tliis, there is also a bud (or buds), either 

 visible, or in a rudimentary state, formed in the axil of each 

 leaf 



a. These axillary buds are generally visible, eitlier before or after the leaf has 

 fallen. In some plants, however, they seldom appear; but their existence is 

 inferred from the fact, tliat even in such cases, they are occasionally developed in 

 extraordinary' circumstances. 



22. Each bud is a distinct individual, capable of an independ- 

 ent existence, in favorable circumstances, although severed from 

 the parent slock. 



a. The common practice of propagation by layers, offsets, engrafting, and 

 budding, is both a result and a proof of this principle. A plant may be, and 



