THE MORPHOLOGICAL COMPOSITION OF PLANTS. 77 



which, not drawing nutriment from roots, have their parts 

 much less mutually dependent; and are therefore capable of 

 showing more clearly, how any part may remain an append- 

 age or may become the parent of append- 

 ages, according to circumstances. In the 

 annexed Fig. 130, representing a branch of 

 Ptilota plumosa, we see how a wing grows 

 into a wing-bearing branch if its nutrition 

 passes a certain point. This form, so strik- 

 ingly like that of the feathery crystallizations /jo 

 of many inorganic substances, implies that, 

 as in such crystallizations, the simplicity 

 or complexity of structure at any place 

 depends on the quantity of matter that has to 

 be arranged at that place in a given time.* 



Hence, then, we are not without an interpretation of those 

 over-developments which the phamogamic axis occasionally 

 undergoes. Fig. 104, represents the phamogamic bud in its 

 rudimentary state. The lateral process b, which ordinarily 

 becomes a foliar appendage, differs very little from the 

 terminal process c, which is to become an axis — differs 

 mainly in having, at this period when its form is being 

 determined, a smaller bulk. If while thus undifferentiated, 

 its nutrition remains inferior to that of the terminal process, 

 it becomes moulded into a part that is subordinate to the 

 general axis. But if, as sometimes happens, there is supplied 

 to it such an abundance of the materials needful for growth, 

 that it becomes as large as the terminal process; then we 



* How the element of time modifies the result, is shown by the familiar 

 fact that crystals rapidly formed are small, and become relatively large when 

 left to form more slowly. If the quantity of molecules contained in a solution 

 is relatively great, so that the mutual polarities of the molecules crowded 

 together in every place throughout the solution are intense, there arises a 

 crystalline aggregation around local axes ; whereas, in proportion as the local 

 action of molecules on one another is rendered less intense by their wider 

 dispersion, they become relatively more subordinate to the forces exerted on 

 them by the larger aggregates of molecules that are at greater distances, and 

 thus are left to arrange themselves round fewer axes into larger crystals. 



