ORGANS or NUTRITION. 



101 



that their petiole or stalk is dilated and membranous, like- 

 the inner scales of the bud; and, finally, leaves perfect in all 

 their parts complete the series of transitions." The scales thus 

 shown to be modified leaves may be formed either of one or of 

 more than one of the parts of a leaf; and the bud receives 

 different names accordingly. Thus, if the scales are formed by 

 the lamina or flattened foliaceous part, as in Daphne Mezereum 

 the bud is called /o//aceo«s ,- if, by expansions of the Ijase of the 

 petiole or leaf-stalk, as in the Walnut-tree, petiolaceous ; if by 

 the stipules, or lateral leafy expansions of the petiole, as in the 

 Magnolia, stipidaceous ; if by both stipules and the petiole com- 

 bined, as in the common J^lnm, fulcraceous. 



As soon as the laminse of the leaves in the bud have acquired 

 a certain size, they become variously folded or rolled on one 

 another, by which they adapt themselves to its rounded form 

 and small space. This arrangement of the leaves in the bud is 

 called vernation or prcBfoliation. There are various modifications 

 of this, each of which is distinguished by a particular name. 

 These will be described hereafter, when treating of the leaves. 



The bud, as we have seen, contains all the elements of a stem 

 or a branch (Jig. 192); in fact, it is really the first stage in the 

 development of such parts, the axis p^ igg^ p-^ J94_ 

 being here so short that the rudimentary 

 leaves are closely packed together, and 

 thus overlap each other (Jig. 193). AYhen 

 growth commences in the spring, or 

 whenever vegetation is reanimated, the 

 internodes between the leaves become 

 developed, and these therefoi*e become 

 separated from each other (^fig. 194, c), 

 and thus the stem increases in length, or 

 a branch is formed. In other words, the 

 leaves, c, which in a bud state overlap 

 each other and surround a growing point 

 or axis, by the elongation of the inter- 

 nodes of that axis become separated and 

 dispersed over a branch or an elongation 

 of the stem, much in the same way as Fig. 193. a shoot one year 

 the joints of a telescope become separated wiVh^termfnaVbud.'^frscars 



produced by the falling off 

 of the bud-scales of the pre- 

 vious year ; b. Scars pro- 

 duced by the falling oft of 

 the petioles of the leaves of 

 the present year, with buds, 



c. in their axils Fig. lt)4. 



Diagram to illustrate the 

 growth of the shoot from 

 the bud. c. c, c. The nodes 

 where the leaves are situ- 

 ated, d, d. The internodes 

 developed between them. 



from each other by lengths of tube when 

 it is drawn out. The branch therefore, 

 like the bud from which it is formed, ne- 

 cessarily contains the same parts as the 

 axis upon Avhich it is placed, and these 

 parts are also continuous with that axis, 

 with the exception of the pith, which, 

 although originally continuous in the 

 bud state, ultimately becomes separated 

 H 3 



