534 
Notices of Boohs. 
[October, 
If one of the young seedlings became sickly or was in any way 
injured it was pulled up and thrown away, as well as its antago- 
nist or. the opposite side of the same pot. 
“ As a large number of seeds were placed on the sand to 
germinate, many remained after the pairs had been selected ; 
these were soon crowded together on the opposite sides of one 
or two rather large pots, or sometimes in two long rows out of 
doors. In these cases there was the most severe struggle for 
life among the crossed seedlings on one side of the pot and the 
self-fertilised seedlings on the other side, and between the two 
lots which grew in competition in the same pot. A vast number 
soon perished, and the tallest of the. survivors on both sides when 
fully grown were measured. Plants treated in this manner were 
subjected to nearly the same conditions as those growing in a 
state of Nature which have to struggle to maturity in the midst 
of a host of competitors.” 
Sometimes the seeds, instead of being previously allowed to 
germinate on damp sand, were sown at once on opposite sides 
of pots, and the plants measured when fully grown. This plan 
Mr. Darwin pronounces less accurate, as the seeds sometimes 
germinated more quickly on one side than the other. He con- 
siders, however, that it was necessary thus to proceed in the case 
of some few species, “ as certain kinds of seeds would not 
germinate well when exposed to the light.” We should suggest 
that such seeds might have been covered with a plate of blue 
glass, since blue light — though not favourable to plants in the 
later stages of their life — undoubtedly promotes germination. 
Every precaution was taken that the two classes of seedlings 
under comparison should in all other respedls be precisely on an 
equality. The soil was evenly and thoroughly mixed, the supply 
of water and the exposure to light were the same. Yet, as we 
have already intimated, the self-fertilised plants, when carefully 
weighed and measured, were decidedly inferior to the crossed. 
Hence Mr. Darwin is perfectly justified in the inference that 
cross-fertilisation is generally beneficial and self-fertilisation in- 
jurious. “ That certain plants,” he remarks, “ such as Cyclamen 
persicum , &c., which have been naturally cross-fertilised for many 
or all previous generations, should suffer to an extreme degree 
from a single adt of self-fertilisation is a most surprising fadt. 
Nothing of the kind has been observed in our domestic animals ; 
but then we must remember that the closest possible inter- 
breeding between such animals — that is, between brothers and 
sisters — cannot be considered as nearly so close a union as that 
between the pollen and the ovules of the same flower. Whether 
the evil from self-fertilisation goes on increasing during suc- 
cessive generations is not as yet known, but we may infer from 
my experience that the increase, if any, is far from rapid. After 
plants have been propagated by self-fertilisation for several gene- 
rations, a single cross with a fresh stock restores their pristine 
