206 NATURAL HISTORY OF SELBORNE. 
in some of tlie lowest and meanest thatched cottages. Now as 
these eight pairs, allowance being made for accidents, breed 
yearly eight pairs more, what becomes annually of this increase ; 
and what determines every spring which pairs shall visit us, and 
reoccupy their ancient haunts ? 
Ever since I have attended to the subject of ornithology, I 
have always supposed that that sudden reverse of affection, that 
strange avriaro^yY], which immediately succeeds m 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 favourite 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. Whe- 
ther 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 XL. To the Hon. DAINES BARRINGTON. 
DEAR SIR, Selborne, June 2, 1778. 
The standing objection to botany has always been, that it is a 
pursuit which amuses the fancy and exercises the memory, with- 
out improving the mind or advancing any real knowledge : and, 
where the science is carried no further than a mere systematic 
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 hst of names ; he should study plants philo- 
sophically, should investigate the laws of vegetation, should 
examine the powers and virtues of efficacious herbs, should pro- 
mote their cultivation ; and graft the gardener, 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 system should be subser- 
vient to, not the main object of, pursuit. 
Vegetation is highly worthy of our attention ; and in itself is 
