228 HOW PLANTS GKOW. 



changes are carried on by cell-division, again and again repeated, 

 the vessels being formed from the cells in the manner already- 

 described. 



During this differentiation of the embryo into "regions," it 



begins to assume a definite shape — i.e.^ it takes on the appearance 



of a miniature plant, with root, stem, and leaves. The lower end 



— />., the end next the micropyle — is first developed on the sus- 



pensor, and is called the Radicle, which is invariably, in the mature 



embryo, close to the micropyle ; this is the future Root. At the 



other end of this central axis is the Plumule, a tiny bud, destined 



to form the growing Stem ; on the centre of the axis are seen two 



small protuberances, gradually assuming a bud-like and then a 



leaf-like form. These are the Cotyledo?ts, or nursing-leaves, or 



seed-leaves — the first leaves of the plant. If there be two (as in 



Bean or Buttercup) the future plant comes under the class of 



Dicotyledons ; if only one (as in Lily or Wheat), it will belong to 



the Monocotyledons. 



We spoke just now of the Endosperm or Albumen that fed 

 the growing Embryo. This brings us to our final step in the 

 passage of the cell up to the plant : — 

 (r) Germination. 



If all the endosperm be absorbed by the embryo as it grows, 

 then the ripe embryo — i.e., the embryo inside the seed — is exalbu7?ii- 

 nous — without albumen, and the embryo entirely fills the seed, as 

 in Bean ; if part only be consumed, the ripe embryo will still 

 possess some, and is albuminous, as in Buttercup and Wheat. 

 These two terms are usually applied to the seed rather than to the 

 embryo. 



This Albumen is the mealy part in the wheat-grain, the oily 

 part in castor-oil seed, the hard white part in cocoa-nut, and the 

 hard brown part in coffee-seed, which we grind down to the well- 

 known and much-approved domestic powder. 



The difi'erence between the albuminous seed of Buttercup and 

 the exalbuminous seed of Bean is mainly this: — In the former, the 

 embryo/^^^i" on the albwjieti, which enables it during germination to 

 develop its root and stem, and after germination, its plumule ; in the 

 latter, the Qmbryo feeds on part of itself , the Cotyledons (which are 

 masses of nutritive cells) enabling it to develop both radicle and 



