REVIEWS AND BOOK NOTICES. 631 
logical connexion with other plants must be sought for in the most 
distant past ages of geological development. 
Constancy of character, as Mr. Darwin has said,* is what is 
chiefly valued and sought after by naturalists; that is to say nat- 
uralists wish to find s i i 
selves to defining and registering the degrees and limits of that 
gradation. The ultimate natural arrangement will often be devoid 
at 
Ap be discovered, and will require the modification of the system. 
natural system is directed, as we have seen, to the discovery of 
From paying too much attention toa classification by types, i.e., 
by selecting one typical form and grouping around it allied forms, 
Professor Jevons believes that “a certain laxity of logical method 
is thus apt to creep in, the only remedy for which will be the 
frank recognition of the fact that according to the theory of heredi- 
tary descent, the gradation of characters is probably the rule, and 
the precise demarcation between groups the exception.” 
The author agrees with those naturalists who regard the exist- 
ence of any such groups as genera and species as “an arbitrary 
creation of the naturalist’s mind ;” an important result of the estab- 
lishment of the theory of evolution being “to explode all notions 
Gt re ERSE 
*‘ Descent of Man, vol. i, p- 214. 
+‘ Laws of Botanical Nomenclature,’ p. 16. 
