8 



knows it to exist. However difBcult it may be, in some 

 instances, to distiaguish aright between species and 

 varieties, as rigidly defined, there is an instinct within 

 us which often recognizes the latter, even at first sight, 

 as unmistakeably such : and in these cases, a well-edu- 

 cated eye, although of course occasionally deceived, will 

 not often be foimd to err. 



In the vegetable world this proneness to variation is 

 self-evident; and botanists innumerable, who have in- 

 vestigated the causes on which the modifications of cer- 

 tain plants have been presumed to depend, have not 

 been behindhand in acknowledgiag it. Soil, climate, 

 altitude, and a combination of other circumstances and 

 conditions, have been successively taken into account, 

 and to each an amount of disturbing influence (more or 

 less, as the case may be) has been conceded. " The 

 more powerfiil agents," writes Professor Henfrey, " en- 

 force their general laws, but every little local action 

 asserts its qualifying voice; and we see that aU these 

 irregularities and uncertainties (as we in our ignorance 

 call them, and complain of) are necessary and important 

 parts of a great whole, — are but isolated features of a 

 comprehensive plan, in accordance with which all work 

 in concert to bring about that change absolutely indis- 

 pensable to the existence of animal and vegetable life 

 upon the earth's surface, and that variety of conditions 

 by which is ensured a fittiug abode for each kind of its 

 multifarious and diversified inhabitants." 



Whilst exploring the barren moor, or bleak upland 



