ctly what the checks are even in a single instance. Nor will
this surprise any one who reflects how ignorant we are on this head,
even in regard to mankind, although so incomparably better known than
any other animal. This subject of the checks to increase has been ably
treated by several authors, and I hope in a future work to discuss it at
considerable length, more especially in regard to the feral animals of
South America. Here I will make only a few remarks, just to recall to
the reader's mind some of the chief points. Eggs or very young animals
seem generally to suffer most, but this is not invariably the case. With
plants there is a vast destruction of seeds, but from some observations
which I have made it appears that the seedlings suffer most from
germinating in ground already thickly stocked with other plants.
Seedlings, also, are destroyed in vast numbers by various enemies; for
instance, on a piece of ground three feet long and two wide, dug and
cleared, and where there could be no choking from other plants, I marked
all the seedlings of our native weeds as they came up, and out of 357
no less than 295 were destroyed, chiefly by slugs and insects. If turf
which has long been mown, and the case would be the same with turf
closely browsed by quadrupeds, be let to grow, the more vigorous plants
gradually kill the less vigorous, though fully grown plants; thus out of
twenty species grown on a little plot of mown turf (three feet by four)
nine species perished, from the other species being allowed to grow up
freely.

The amount of food for each species, of course, gives the extreme limit
to which each can increase; but very frequently it is not the obtaining
food, but the serving as prey to other animals, which determines the
average number of a species. Thus, there seems to be little doubt that
the stock of partridges, grouse, and hares on any large estate depends
chiefly on the destruction of vermin. If not one head of game were shot
during the next twenty years in England, and, at the same time, if no
vermin were destroyed, there would, in all probability, be less game
than at present, although hundreds of thousands of game animals are now
annually shot. On the other hand, in some cases, as with the elephant,
none are destroyed by beasts of prey; for even the tiger in India most
rarely dares to attack a young elephant protected by its dam.

Climate plays an important part in determining the average numbers of