“194 THE NATURAL HISTORY OF SELBORNE. 
Ever since I have attended to the subject of ornithology, I 
have always supposed that that sudden reverse of affection, 
that strange parental dislike, which immediately succeeds in 
the feathered kind to the most passionate fondness, is the 
occasion of an equal dispersion of birds over the face of the 
earth. Without this provision one favorite district would be 
crowded with inhabitants, while others would be destitute and 
forsaken. But the parent birds seem to maintain a: jealous 
superiority, and to oblige the young to seek for new abodes ; 
and the rivalry of the males, in many kinds, prevents their 
crowding the one on the other. Whether the swallows and 
house-martins return in the same exact number annually is not 
easy to say, for reasons given above ; but it is apparent, as I 
have remarked before in my monographies, that the numbers 
returning bear no manner of proportion to the numbers retiring. 
LETTER XXXVI. 
SELBORNE, June 2nd, 1778. 
The standing objection to botany has always been, that it is 
a pursuit that amuses the fancy and exercises the memory, 
without improving the mind or advancing any real knowledge ; 
and, where the science is carried no farther than a mere sys- 
tematic classification, the charge is but too true. But the 
botanist that is desirous of wiping off this aspersion should be 
by no means content with a list of names; he should study 
plants philosophically, should investigate the laws of vegeta- 
tion, should examine the powers and virtues of efficacious 
herbs, should promote their cultivation; and graft the gar- 
dener, the planter, and the husbandman, on the phytologist. 
Not that system is by any means to be thrown aside; without 
system the field of Nature would be a pathless wilderness ; but 
