THE MORPnOLOGICAL COMPOSITION OF PLANTS. 63 



Hon of the leaf-producing parts from the root-producing 

 parts; a greater development of that connecting portion of 

 the successive fronds, by which they are kept in communica- 



tion with the roots, and raised above the ground; and a con- 

 sequent increased differentiation of such connecting portion 

 from the parts attached to it. And this lateral bulging of 

 the axis, directly or indirectly consequent on its functions as 

 a support and a channel, being here unrestrained by the 

 early-formed fronds folded round it, goes on without the 

 bursting of these. Hence arises a leading character of what 

 is called exogenous growth — a growth which is, however, still 

 habitually accompanied by exfoliation, in flasks, of the outer- 

 most layers, continually being cracked and split by the accu- 

 mulation of layers within them. And now if we ex- 

 amine plants of the exogenous type, we find among them many 

 . displaying the stages of this metamorphosis. In Fig. 95, is 

 shown a form in which the continuity of the axis with the 

 mid-rib of the leaf, is manifest — a continuity that is con- 

 spicuous in the common thistle. Here the foliar expansion, 

 running some distance down the axis, makes the included 

 portion of the axis a part of its mid-rib; just as in the ideal 

 types above drawn. By the greater growth of the internodes, 



