245 
The Rhizophore of Selaginella. 
special and distinct characteristics which are not referable in their 
entirety to any of the existing types. Now, the organs whose mor¬ 
phological value and origin are doubtful or unknown, are in a very 
small minority (I have cited most of them above). I ask, therefore, 
which is the more likely theory : (1) that certain specialised groups 
have produced new types of organs after the lapse of an imme¬ 
morial past of evolution in which we can find no trace of such, or 
Fig. 16. Portion of shoot of S. inequalifolia shewing rhizophores arising at 
points of forking. 
(2) that here and there in certain groups some already-existing 
organs have become specialised and modified to such a degree as to 
render them no longer recognisable as such, and hence, apparently 
new and distinct in type ? For my part, the second of these 
hypotheses is the only tenable one. 
