436 Darwin, and after Darwin. 
precarious,—and this in so high a degree that any conclusions 
raised on such premises are not entitled to be deemed for- 
midable *. 
Turning now to plants, the principal and the ablest 
opponent of the theory of evolution is here unquestionably 
Mr. Carruthers* The difficulties which he adduces may be 
classified under three heads, as follows :— 
1. There is no evidence of change in specific forms of 
extsting plants. Not only are the numerous species of 
plants which have been found in Egyptian mummies in- 
distinguishable from their successors of to-day; but, what 
is of far more importance, a large number of our own 
indigenous plants grew in Great Britain during the glacial 
period (including under this term the warm periods between 
those of successive glaciations), and in no one case does it 
appear that any modification of specific type has occurred. 
This fact is particularly remarkable as regards leaves, 
because on the one hand they are the organs of plants which 
are most prone to vary, while on the other hand they are 
likewise the organs which lend themselves most perfectly 
to the process of fossilization, so that all details of their 
structure can be minutely observed in the fossil state. Yet 
the interval since the glacial period, although not a long one 
geologically speaking, is certainly what may be called an 
appreciable portion of time in the history of Dicotyledonous 
plants since their first appearance in the Cretaceous epoch. 
Again, if we extend this kind of enquiry so as to include the 
world as a whole, a number of other species of plants dating 
from the glacial epoch are foynd to tell the same story— 
notwithstanding that, in the opinion of Mr. Carruthers, they 
must all have undergone many changes of environment 
' See Lay Sermons, Lecture on Geological Reform. 
? See especially the following Presidential addresses :- Gcol. Assoc, 
Nov. 1876; Section D. Brit. Assoc., 1886; Lin. Soc., 1890. 
