196 DARWINIAN A. 



selection. The former Las never yet been shown to 

 have its canse in " external influences," nor to occur 

 at random. As we have elsewhere insisted, if not 

 inexplicable, it has never been explained ; all we can 

 yet say is, that plants and animals are prone to vary, 

 and that some conditions favor variation. Perhaps in 

 this Dr. Falconer may yet find what he seeks : for 

 " it is difficult to believe that there is not in [its] na- 

 ture a deeper-seated and innate principle, to the opera- 

 tion of which natural selection is merely an adjunct." 

 The latter, which is the ensemble of the external in- 

 fluences, including the competition of the individuals 

 themselves, picks out certain variations as they arise, 

 but in no proper sense can be said to originate them. 

 2. Although we are not quite sure how Dr. 

 Falconer intends to apply the law of phyllotaxis to 

 illustrate his idea, we fancy that a pertinent illustra- 

 tion may be drawn from it, in this way. There are 

 two species of phyllotaxis, perfectly distinct, and, we 

 suppose, not mathematically reducible the one to the 

 other, viz. : (1.) That of alternate leaves, with its varie- 

 ties ; and (2.) That of verticillate leaves, of which op- 

 posite leaves present the simplest case. That, although 

 generally constant, a change from one variety of alter- 

 nate phyllotaxis to another should occur on the same 

 axis, or on successive axes, is not surprising, the dif- 

 ferent sorts being terms of a regular series although, 

 indeed, we have not the least idea as to how the change 

 from the one to the other comes to pass. But it is 

 interesting, and in this connection perhaps instructive, 

 to remark that, while some dicotyledonous plants hold 

 to the verticillate, i. e., opposite-leaved phyllotaxis 



