of the Permanence of Varieties. 197 
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 continu- 
ally 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. or the former is the closest 
possible kind of close breeding. Upon this ground such 
varieties may be expected ultimately to die out; but “ the 
mills of the gods grind so exceedingly slow,” that we cannot 
say that any particular grist has been actually ground out 
under human observation. 
If it be asked how the asserted principle is proved or made 
probable, we can here merely say that the proof is wholly infe- 
rential. But the inference is drawn from such a vast array of 
facts that itis well nigh irresistible. It is the legitimate expla- 
nation of those arrangements in nature to secure cross-fertiliza- 
tion in the species, either constantly or occasionally, which are 
so general, so varied and diverse, and, we may add, so exquisite 
and wonderful, that, once propounded, we see that it must be 
true. What else, indeed, is the meaning and use of sexual 
reproduction? Not simply increase in numbers; for that is 
otherwise effectually provided for by budding propagation in 
plants and many of the lower animals. There are plants, 
indeed, of the lower sort, in which the whole multiplication 
takes place in this way, and with great rapidity. These also have 
sexual reproduction ; but in it two old individuals are always 
destroyed to make a single new one! Here propagation 
diminishes the number of individuals 50 per cent. Who can 
suppose that such a costly process as this, and that all the 
exquisite arrangements for cross-fertilization in hermaphrodite 
plants, do not subserve some most important purpose? How 
and why the union of two organisms, or generally of two very 
minute portions of them, should reenforce vitality, we do not 
know and can hardly conjecture. But this must be the mean- 
ing of sexual reproduction. 
The conclusion of the matter from the scientific point of view 
is, that sexually propagated varieties, or races, although liable 
to disappear through change, need not be expected to wear 
out, and there is no proof that they do—but that non-sexually 
propagated varieties, though not lable to change, may theo- 
retically be expected to wear out, but to be a very long time 
about it. 
Ann. & Mag. N. Hist. Ser. 4. Vol. xv. 14 
