$80 PRINCIPLES OF BOTANY, ETC. 
might, against our will, give rise to bastard produc. 
tions, which in a natural state could not have hap- 
pened. We will certainly by and by get acquainted 
with some plants which are never found originally 
growing wild, but owe their existence entirely to 
the botanic garden. 
Our numberless varieties of fruit, we owe un- 
doubtedly to some kind of bastard generation, and 
many of them, which we consider as proper pecu- 
liar genera, are perhaps only such preternatural hy- 
brids. Ido not think it, therefore, at all impro- 
bable, that Pyrus disica, Pollveria, and prunifolia, 
owe their existence to such circumstances. 
§ 353. 
But even should it remain uncertain, whether 
some plants have arisen entirely from a commix- 
ture of various species, we may perhaps, from the 
observations hitherto collected on the subject, be 
enabled to make a more certain conclusion, with 
respect to the former state of our globe, and the 
probability that great revolutions have taken place 
in the vegetable world. 
Various, and often very fanciful ideas, have been 
formed by philosophers, on the origin of our globe, 
and the changes it has undergone. Every one sup- 
poses he has given a true explanation, but upon the 
whole, we have not come nearer the truth. And 
indeed we will never have the satisfaction to form a 
true idea of the formation of the earth, nor ever be 
able to fix the periods with certainty, when all the 
preat revolutions in it happened. ; 
3 For 
