ENATION OF LEAF 143 
morphological experience. Therefore the validity of the strobiloid theory 
is not open to 4 priori objection. The real question is whether those 
processes which are seen to have been in operation elsewhere did actually 
take part in the production of the Pteridophyte strobilus as it is now 
seen? The applicability of the theory to the various known types of 
Pteridophytes will be the true test of its validity. This will be carried 
out in detail in the second part of this work, so far as the very imperfect 
evidence will allow. In questions such as this of the origin of the shoot, 
it is desirable to take the simplest possible reading of the facts as the 
basis of an opinion: on this ground the theory of enation, as accounting 
for the origin of the appendages of the strobilus, seems to be preferable 
to any phytonic theory. It has been remarked that the .strobiloid theory 
involves “tremendous morphological assumptions in the way of the origin 
of new organs” (Tansley, Mew Phytologist, 1907, p. 28, etc.): the only 
assumption, however, which is apparent to the mind of its author. is that 
the order and mode of origin of the appendicular parts in the course of 
Descent has been that which is actually seen in their individual develop- 
ment. They are formed by enation from the axis now, and it is held 
that they originated in the first instance in the same way. 
