CHAPTER III. 



THE MORPHOLOGICAL COMPOSITION OF PLAKTS, 

 CONTINUED. 



§ 187. That advanced composition arrived at in the 

 Acrogens, is carried still further in the Endogens and Exo- 

 gens. In these most-elevated vegetal forms, aggregation 

 of the third order is always distinctly displayed ; and aggre- 

 gates of the fourth, fifth, sixth, &c, orders are very common. 



Our inquiry into the morphology of these flowering 

 plants, may be advantageously commenced by studying the 

 development of simple leaves into compound leaves. It is 

 easy to trace the transition, as well as the conditions under 

 which it occurs ; and tracing it will prepare us for under- 

 standing how, and when, metamorphoses still greater in de- 

 gree, take place. 



§ 188. If we examine a branch of the common bramble, 

 when in flower or afterwards, we shall not unfrequently find 

 a simple or undivided leaf, at the insertion of one of the 

 lateral flower-bearing axes, composing the terminal cluster of 

 flowers. Sometimes this leaf is partially lobed ; sometimes 

 cleft into three small leaflets. Lower down on the shoot, if 

 it be a lateral one, occur larger leaves, composed of three 

 leaflets ; and in some of these, two of the leaflets may be 

 lobed more or less deeply. On the main stem, the leaves, 

 usually still larger, will be found to have five leaflets. Sup- 



