Theory of Antithetic Alternation of Generations. 123 
“ the appendages actually appear in the ontogeny by enation” (p. 141). 
This argument is stated several times, and is evidently regarded as 
of primary importance. It is really difficult to know how to meet 
such a contention except by a blank refusal to accept the validity 
of so crude an application of the facts of ontogeny to the elucidation 
of a phylogenetic problem. We had supposed that modern mor¬ 
phologists had agreed to abandon this kind of method altogether. 
Let us see where it would lead us in the first case that comes to 
mind. The sporangia of Leptosporangiate Ferns undoubtedly 
“ appear in the ontogeny by enation.” Would Professor Bower 
therefore conclude that that was their origin in evolution, or even 
that the ontogenetic fact afforded any presumption in such a 
direction ? We know, on the contrary, that he regards this parti¬ 
cular type of sporangium as having had a long ancestral history, 
and as ultimately derivable from a portion of the continuous 
sporogenous layer of a Bryophytic sporogonium. Similarly the 
opponents of the “ enation ” theory of the phylogenetic origin of 
the leaf believe that the leaves of Pteridophytes originated from 
pre-existent structures, and cannot possibly accept their onto¬ 
genetic origin by enation as affording any presumption to the 
contrary. 
At the close of the chapter (p. 143) the author appears in the 
character of an innocent person unjustly accused of making 
“ tremendous morphological assumptions in the way of the origin of 
new organs.” His defence is that “ the only assumption apparent 
to the mind of its author [i.e., of the strobiloid theory], 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 
development.” Instructive light is thrown on the plea that such 
an assumption is justifiable by a statement which appears on p. 152 
in another connexion. “ It is often assumed ” says Professor 
Bower, “ that the vegetative leaf was pre-existent in descent to 
the appendages of the strobilus, the mind naturally translating the 
successive events of the individual life directly into the history of its 
evolutionary organisation ” (italics ours), and he goes on to show 
that such an assumption is illegitimate. The author here, and in 
other similar passages, directly contributes to his own conviction 
on the charge of making assumptions, which he himself appears to 
recognise as illegitimate, and which it is scarcely unfair to describe 
as “tremendous,” 
We think that the readers of a work of the size and scope of 
Professor Bower’s book, into which the controversial element 
necessarily enters to a large extent, have good reason to complain 
that the author has not devoted a great deal more time and 
space to considering the objections to his theory. These objections 
may be roughly classed as “ general ” and “ special.” Of the 
former we may distinguish the following 
(1.) It is a priori in the highest degree unlikely that so 
fundamentally important an organ as the foliage leaf of the 
vascular plant appeared in descent as an “ enation ” from the 
surface of a cylindrical body of different morphological nature. 
There is no well-established case of any such origin of an organ of 
the importance and with the potentialities of the leaf in the evolu¬ 
tionary history of the plant-kingdom. That enation of hairs and 
prickles has frequently occurred is true ; but the potentiality of 
