146 THE STRUCTURE OF FLOWERS. 



special vital action at the place. If, however, the same 

 place be induced to secrete bj constantly repeated irritations, 

 as the same flower is repeatedly visited over and over again 

 before it fades, and the flowers of its ofl^spring have to un- 

 dergo the same process, year after year, generation after 

 generation, I think it is at least a reasonable surmise that 

 there will at last ensue a permanent flow of fluid to the place, 

 with a corresponding modification of structure, and so the 

 nectary becomes established. If, however, from any cause 

 the flowers become neglected, then the nectaries degenerate 

 and ultimately disappear. 



Apart from some general theory of the kind proposed, it 

 is impossible to assign a reason for glands appearing at all 

 sorts of places in flowers. A theory to be worthy of accep- 

 tance must meet all cases, if possible, and I maintain that 

 the one I propose is compatible with every observation that 

 has been made in flowers.* 



* I would suggest a similar origin for the insectivorous pitchers of 

 Nepenthes. They originate, as Sir J. D. Hooker has shown, from water- 

 glands. The effort to dispose of water brought up by the fibro-vascular 

 cord keeps the tissue of water-glands at the extremity of a cord in a 

 state of plethora, thereby somewhat arresting any change of form and 

 retaining the cells in the very characteristic merismatic stage. And if 

 it now meet with an external irritation from insects attracted by the 

 escape of fluids a further response to their influence begins, and the 

 wonderful structures we are familiar with in the pitchers of Nepenthes 

 are the final result. 



I see no greater difficulty in conceiving of such an origin than in 

 any other complex structure, such as the human eye. If the latter could 

 originate from an epidermal cell sensitive to light only, and by succes- 

 sive increments, traceable more or less distinctly through the various 

 strata of animal life, finally reach the highest and most complex form 

 of that of man, there is nothing inconceivable in the growth and 

 differentiation of a pitcher in response to an external stimulus. 



What I cannot conceive of is, that any organ has ever originated 

 ■without a definite stimulating cause acting persistently in one and the 



