304 Canadian Record of Science. 



The various transformations which we have studied in 

 Nephrolepis afford direct and positive proof of the origin of 

 compound leaves by modification of the simple, primary form 

 as stated by Goebel, 1 who illustrates the general course of de- 

 velopment by the very striking variations exhibited in Anaden- 

 drum medium ; and by Ward, who has shown that such a 

 course of development is also exhibited in fossil forms. But 

 Goebel directs attention to the general effect of light and shade 

 which operate in such wise that conditions of shade always 

 tend to the development of rounded and simplified, juvenile 

 forms, so that the effect of light would be to reduce the area 

 with a tendency to splitting up or compounding. 2 This is ex- 

 actly in accord with the changes in Nephrolepis piersoni and 

 the conditions under which such changes arise, since it is 

 found that it demands for its best development, an abundance 

 of light. 



The compounding of the leaf in Pierson's fern, being in 

 itself an expression of highly developed vegetative powers, is 

 intimately associated with other changes of a no less striking 

 and significant character. The almost complete obliteration 

 of the sporogenous tissue, and hence obliteration of the usual 

 reproductive function which survives mainly in unmodified 

 parts, is in precise accord with Bower's theory respecting the 

 origin of the sporophyte, and it is to be attributed to "correla- 

 tion" with the assimilative tissue. But as already seen, Pierson's 

 fern does show a tendency to the formation of sporogenous 

 tissue even on completely transformed parts, thus indicating 

 that with greater stability in the variety, it becomes possible 

 for this reproductive tissue to be reestablished. This is made 

 clear in the case of Foster's fern, in the fact that the sporoge- 

 nous tissue not only persists from the first, but that the plant 

 shows a corresponding diminution in size ; so that as between 

 the two forms, it comes to be a simple case of relative arrest 

 through correlation. We may therefore expect to find that 

 these two plants exhibit different degrees of stability with re- 

 spect to their special forms, and such differences do exist to 



1. Organography, 158. 



2. Ibid. 242. 



