310 J.D. Hooker, Introductory Essay to the Flora of Tasmania, 
35. From the sum then of our theories, as arranged in accord: 
ance with ascertained facts, we may make the following assump 
tions :—That the principal recognized families of plants which 
al changes. at of these types some have been tra 
or have migrated, from one hemisphere to another. That it 
. o . So . . . . . nl 
owe their different forms to the variation of individuals, and the 
power of limiting them into genera and species to the destruc: 
tion of some of these varieties, ete., and the increase of individ 
the present state of science, botany throws no light whatever 
Regarded from the classificator point of view, the geo 
gressive a both because the earliest ascertain 
are of such high and complex organization, and pieden be 
-4re no known fossil plants which we can certainly assume to a 
i 
* In considering the relative amount and rate at which different plants vi bat ‘ 
Should be remembered that we habitually estimate them not only loosel 
P : rman 
nee enables us to study many generations of an annual et ri a. 
But, viii, p, 
