It is possible, however, that man, by long-continued
selection, may have given to the grains of the cereals a greater amount
of starch or other matter, than the seedlings can utilise for their
growth. There can be little doubt, as Humboldt long ago remarked, that
the grains of cereals have been rendered attractive to birds in a degree
which is highly injurious to the species.) Nor can this difference in
the growth of the seedling turnips be attributed to the heavier seeds
having been of crossed, and the lighter of self-fertilised origin, for
it is known that plants belonging to this genus are habitually
intercrossed by insects.
With respect to the relative period of germination of crossed and
self-fertilised seeds, a record was kept in only twenty-one cases; and
the results are very perplexing. Neglecting one case in which the two
lots germinated simultaneously, in ten cases or exactly one-half many of
the self-fertilised seeds germinated before the crossed, and in the
other half many of the crossed before the self-fertilised. In four out
of these twenty cases, seeds derived from a cross with a fresh stock
were compared with self-fertilised seeds from one of the later
self-fertilised generations; and here again in half the cases the
crossed seeds, and in the other half the self-fertilised seeds,
germinated first. Yet the seedlings of Mimulus raised from such
self-fertilised seeds were inferior in all respects to the crossed
seedlings, and in the case of Eschscholtzia they were inferior in
fertility.
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