THE MORPHOLOGICAL COMPOSITION OF PLANTS. 63 



tion 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, 



