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Darwiniana; Essays and Reviews Pertaining to Darwinism by Asa Gray
page 291 of 342 (85%)

But does it follow from this that non-sexually-propagated varieties are
endowed with the same power of unlimited duration that is possessed by
varieties and species propagated sexually--i.e., by seed? Those who think
so jump too soon at their conclusion. For, as to the facts, it is not
enough to point out the diseases or the trouble in the soil or the
atmosphere to which certain old fruits are succumbing, nor to prove that a
parasitic fungus (Peronospora infestans) is what is the matter with
potatoes. For how else would constitutional debility, if such there be,
more naturally manifest itself than in such increased liability or
diminished resistance to such attacks? And if you say that, anyhow, such
varieties do not die of old age--meaning that each individual attacked does
not die of old age, but of manifest disease--it may be asked in return, what
individual man ever dies of old age in any other sense than of a similar
inability to resist invasions which in earlier years would have produced no
noticeable effect? Aged people die of a slight cold or a slight accident,
but the inevitable weakness that attends old age is what makes these slight
attacks fatal.

Finally, there is a philosophical argument which tells strongly for some
limitation of the duration of non-sexually propagated forms, one that
probably Knight never thought of, but which we should not have expected
recent writers to overlook. When Mr. Darwin announced the principle that
cross-fertilization between the individuals of a species is the plan of
Nature, and is practically so universal that it fairly sustains his
inference that no hermaphrodite species continually self-fertilized would
continue to exist, he made it clear to all who apprehend and receive the
principle that a series of plants propagated by buds only must have weaker
hold of life than a series reproduced by seed. For the former is the
closest possible kind of close breeding. Upon this ground such varieties
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