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crossed and 1859 1860 1861 1866
first crossed, and the maximum produced 1869 1872

parent-species 1859 1860 1866 1869 1872
parent species in 1861

error seems to me 1859 1860 1861 1866 1869
serious error here intervene: a plant, 1872

here introduced: a plant to be 1859 1860 1861
here introduced: a plant, to be 1866 1869
OMIT 1872

during several years 1859 1860 1861
OMIT 1866 1869 1872

the primrose and cowslip, which we have such good reason to believe to be 1859 1860 1861
some forms, such as the common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as 1866 1869 1872

only once or twice succeeded in getting fertile seed; as he 1859 1860 1861
OMIT 1866 1869 1872

common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as varieties, 1859 1860 1861
OMIT 1866 1869 1872

together; and 1859 1860 1861
we may doubt whether many other species are really so sterile, when intercrossed, 1866
we may doubt whether many species are really so sterile, when intercrossed, 1869 1872

came to the same concluson in several other analogous cases; it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1859
came to the same conclusion in several other analogous cases; it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1860
came to the same conclusion in several other analogous cases, it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1861
OMIT 1866 1869 1872

unhesitatingly ranks them as varieties. Gärtner, also, makes the rule equally universal; and he disputes the entire fertility of Kölreuter's ten cases. But in these and in many other cases, Gärtner is obliged carefully to count the seeds, in order to show that there is any degree of sterility. He always compares the maximum number of seeds produced by two species when crossed and by their hybrid offspring, with the average number produced by both pure parent-species
in
in
a state of nature. But
a serious
a serious
causes
cause
of error seems to me to be here introduced: a plant to be
hybridised,
hybridised
must be castrated, and, what is often more important, must be secluded in order to prevent pollen being brought to it by insects from other plants. Nearly all the plants
experimented
experimentised
on by Gärtner were potted, and
apparently
apparently
were kept in a chamber in his house. That these processes are often injurious to the fertility of a plant cannot be doubted; for Gärtner gives in his table about a score of cases of plants which he castrated, and artificially fertilised with their own pollen, and (excluding all cases such as the Leguminosæ, in which there is an acknowledged difficulty in the manipulation) half of these twenty plants had their fertility in some degree impaired. Moreover, as Gärtner during several years repeatedly crossed the primrose and cowslip, which we have such good reason to believe to be varieties, and only once or twice succeeded in getting fertile seed; as he found
them
the
common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as varieties, absolutely
sterile,
sterile
together; and as he came to the same concluson in several other analogous cases; it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner
believed.
believes.