| → with twenty-six 1860 1861 1866 1869 1872 |
| judging from the 1859 |
|
| → other parasitic insects. 1861 1866 1869 1872 |
| birds. 1859 1860 |
|
| → OMIT 1861 1866 1869 1872 |
| (whose numbers are probably regulated by hawks or beasts of prey) 1859 1860 |
|
| → parasitic insects would probably increase; 1861 1866 1869 1872 |
| flies would decrease— then cattle and horses would become feral, 1859 |
| flies would decrease— then cattle and horses would became feral, 1860 |
|
|
When I ascertained that these young trees had not been sown or planted, I was so much surprised at their numbers that I went to several points of view, whence I could examine hundreds of acres of the unenclosed heath, and literally I could not see a single Scotch fir, except the old planted clumps. But on looking closely between the stems of the heath, I found a multitude of seedlings and little
which had been perpetually browsed down by the cattle. In one square yard, at a point some hundred yards distant from one of the old clumps, I counted thirty-two little trees; and one of them,
→with twenty-six
rings of growth,
during
years tried to raise its head above the stems of the heath, and had failed. No wonder that, as soon as the land was enclosed, it became thickly clothed with vigorously growing young firs. Yet the heath was so extremely barren and so extensive that no one would ever have imagined that cattle would have so closely and effectually searched it for food. |
|
| Here we see that cattle absolutely determine the existence of the Scotch fir; but in several parts of the world insects determine the existence of cattle. Perhaps Paraguay offers the most curious instance of this; for here neither cattle nor horses nor dogs have ever run wild, though they swarm southward and northward in a feral state; and Azara and Rengger have shown that this is caused by the greater number in Paraguay of a certain fly, which lays its eggs in the navels of these animals when first born. The increase of these flies, numerous as they are, must be habitually checked by some means, probably by
→other parasitic insects. Hence, if certain insectivorous birds
→OMIT
were to
in Paraguay, the
→parasitic insects would probably increase;
and this would
|
