114. A. Gray—Do varieties wear out, or tend to wear out? 
tween 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 con- 
tinue to exist, he made it clear to all who apprehend and receive 
the principle, that a series of plants propagated by buds onl 
must have weaker hold of life than a series reproduced by see 
For 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 exceeding slow ” 
that we cannot say that any particular grist has been actually 
ground out under human observation. 
it be asked how the asserted principle is proved or made 
probable, we can here merely say that the proof is wholly infer- 
ential. But the inference is drawn from such a vast array of 
facts that it is 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 
in this way, and with great rapidity. These also have sexual 
reproduction ; but in it two old individuals are always destroy 
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 subservé — 
some most important purpose? How and why the union of two 
organisms, or generally of two very minute portions of them, 
should re-enforce vitality, we do not know and can hardly con 
jecture. But this must be the meaning of sexual reproduction. 
The conclusion of the matter from the scientific ser 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 
19g varieties, though not liable to change, may theoret 
= y be expected to wear out, but to be a very long time 
about it. 
