246 
W. C. Worsdelt. 
The facts cited above go to shew that there can be no organs at 
the present day which are intermediate in essential nature between 
root and stem or between stem and leaf, &c., but that there may be 
organs which are intermediate in appearance, through possessing 
some of the characters which are typical of quite distinct organs. 
But it is one thing for organs ( e.g., root and shoot) which have for 
ages been differentiated as such to become apparently fused, or 
indistinguishable on the surface (owing to extreme specialisation as 
the result of adaptation to special functions), and quite another 
thing for those same superficially-doubtful organs to represent a 
persistent, undifferentiated, neutral type or a completely new 
departure in the form of something sui generis. I am unable, 
therefore, to accept or understand the position maintained by 
Goebel and others that such indifferent sui generis organs can and 
do exist. Nor can I concur with the method of classifying doubtful 
organs (such as the tubers of Dioscoreaceae and the rhizophore of 
Selaginella ) in terms of the mere appearance which such organs present 
(as regards structure, habit, position, &>c.) to ordinary observation. I 
conceive it to be the duty of the morphologist to set himself firmly 
against any purely descriptive method of the classification of 
structures, his ambition rather being to reach beyond the mere 
appearance and to fathom, if possible, the real nature, i.e., the 
phylogenetic origin, of the structures concerned. 
The rhizophore is an organ confined to the genus Selaginella. 
It occurs, either on the upper or lower surface, or both, at the point 
of branching, of the (usually) dorsiventral stem, and subsequent in 
time to this branching. It rapidly elongates into a root-like organ 
which grows downward to the soil, on reaching which, or slightly 
before, it emits roots close behind its apex which serve to fix the 
plant in the substratum. The rhizophore usually dichotomizes 
before reaching the soil. It is probable that all species produce 
rhizophores and under normal circumstances, it is only through the 
indirect method of rhizophore-formation that roots are ever produced. 
It has been shewn, however, that roots can be induced to form 
directly from the basal ends of stem-cuttings, and the much swollen 
base of the hypocoty! of S. spinulosa also produces endogenous roots 
directly. 
The question is : what morphological value has the rhizophore ? 
for that it must represent either a root, a shoot or a leaf follows 
from what I have already written above. For obvious reasons it 
cannot be a leaf. It is therefore either a root or a shoot. It 
