70 



MORPHOLOGY, OR COMPARATIVE ANATOMY. 



them on the outside are modified leaf-structures, forming scales for 

 the protection of the inner leaves, and destined to fall off when 

 the bud expands. In the early conditions, the flower-bud is essen- 

 tially analogous to a leaf -bud ; but its ultimate history is different, 

 as will be shown hereafter. 



Many of the general characters of huds have been described already, 

 under the head of the stem (pp. 34, 35) ; but there are some other more 

 special peculiarities which require separate treatment here ; and repetition 

 of certain more important facts will not be disadvantageous. 



In all seeds, except those of the few Orders which present an 

 incomplete or acotyledonous embryo, the young plant is possessed, 

 at or soon after the time of germination, of a rudimentary bud, 

 called the plumule, situated at the point of growth of its ascending 

 axis (figs. 120-122). This is the terminal bud of the young 



;. 122. 



Fig. 121. 



Fig. 120. Monocotyledonous embryo of Potamogeton, cut through perpendicularly : a, radicle ; 



b, cotyledon ; c, plumule. 

 Fig. 121. Dicotyledonous embryo of the Bean (Faba), with the cotyledons, b' b', separated : 



a, radicle ; c, plumule. 

 Fig. 122. Diagram of a germinating Dicotyledon, with the plumule or terminal bud between 



the expanded cotyledons. 



plant ; and stems and shoots only retain the power of elongating 

 so long as they possess such a bud at their extremity. When it 

 is removed by artificial means, by frost, or, by metamorphosis, is 

 replaced by a flower, the onward growth of the shoot ceases. 



Axillary buds are the origin of the ramifications of stems. 

 They are developed in the axils of leaves ; and as they unfold into 

 secondary axes, they become the terminal buds of such shoots. 

 Other axillary buds are formed at the nodes of these secondary 

 shoots, to repeat the ramification by developing into tertiary axes 

 according to the type of the species '(see p. 34). 



Adventitious or accidental buds are those which appear, con- 

 trary to the usual order, at indefinite points, unconnected with the 

 axils of leaves. Generally speaking they are abnormal products, 



