| → will almost invariably 1869 1872 |
| almost invariably will 1859 1860 1861 1866 |
|
| → could 1859 1860 1861 1866 1869 |
| (crossing being prevented) could 1872 |
|
| → half-a-dozen 1860 1861 1866 1869 1872 |
| half a dozen 1859 |
|
|
proportional numbers and kinds of trees now growing on the old Indian ruins! |
|
| The dependency of one organic being on another, as of a parasite on its prey, lies generally between beings remote in the scale of nature. This is
the case with those which may
said to struggle with each other for existence, as in the case of locusts and grass-feeding quadrupeds. But the struggle
→will almost invariably
be most severe between the individuals of the same species, for they frequent the same districts, require the same food, and are exposed to the same dangers. In the case of varieties of the same species, the struggle will generally be almost equally severe, and we sometimes see the contest soon decided: for instance, if several varieties of wheat be sown together, and the mixed seed be resown, some of the varieties which best suit the soil or climate, or are naturally the most fertile, will beat the others and so yield more seed, and will consequently in a few years
supplant the other varieties. To keep up a mixed stock of even such extremely close varieties as the
sweet-peas, they must be each year harvested separately, and the seed then mixed in due
otherwise the weaker kinds will steadily decrease in
and disappear. So again with the varieties of
it has been asserted that certain mountain-varieties will starve out other mountain-varieties, so that they cannot be kept together. The same result has followed from keeping together different varieties of the medicinal leech. It may even be doubted whether the varieties of any
of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock
→could
be kept up for
→half-a-dozen
|
