For plants sown by nature generally come up crowded, and are
almost always exposed to very severe competition with one another and
with other kinds of plants. This latter consideration led me to make
some trials, chiefly but not exclusively with Ipomoea and Mimulus, by
sowing crossed and self-fertilised seeds on the opposite sides of large
pots in which other plants had long been growing, or in the midst of
other plants out of doors. The seedlings were thus subjected to very
severe competition with plants of other kinds; and in all such cases,
the crossed seedlings exhibited a great superiority in their power of
growth over the self-fertilised.
After the germinating seedlings had been planted in pairs on the
opposite sides of several pots, the remaining seeds, whether or not in a
state of germination, were in most cases sown very thickly on the two
sides of an additional large pot; so that the seedlings came up
extremely crowded, and were subjected to extremely severe competition
and unfavourable conditions. In such cases the crossed plants almost
invariably showed a greater superiority over the self-fertilised, than
did the plants which grew in pairs in the pots.
Sometimes crossed and self-fertilised seeds were sown in separate rows
in the open ground, which was kept clear of weeds; so that the seedlings
were not subjected to any competition with other kinds of plants.
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