248 Notice of Dr. Hooker’s Flora of New Zealand. 
or necessity arises for combining results, and presenting them in that 
systematic form which can alone render them available for the purpo- 
ses of science, it becomes necessary for the generalizer to proceed 
upon some determinate principles.” 
The considerations here adduced bear partly in favor of the 
single creation of species of plants, partly on their permanence of 
specific characters from age to age; which are different questions, 
although closely connected. In respect to the first, we have tl 
mere statement of the nature and kind of evidence that is avail- 
view which, by separating the idea of genetic meagre of 
our conception of a species, seems to leave these no gro 
basis of natural history npon a@ priori conceptions, and there 
form” (the definition of the late Dr. Morton), but one Te " 
sented in nature by the perennial succession of essentially 
