THEIR RELATIONS NOT CONSTANT 155 
order of disposition of the parts, or from that structural character which 
has ,been held as typical, are chiefly found where they would on this view 
be theoretically probable, viz. in the Homosporous Pteridophytes. This 
seems to be the natural way of regarding the various types of strobilus 
seen in early Vascular Plants: it is certainly more satisfactory than any 
attempt forcibly to reduce them to conformity with categories based upon 
the study of those plants which represent a later phase of evolution. 
