SELF-FERTILIZATION OF PLANTS. 383 
plants deteriorated, it shows that ‘the difference between self-fertilization and inter- 
crossing was gradually diminishing. Such an effect is due, according to Mr. Darwin, 
to the fact that the intercrossed plants became by close in-breeding more and more 
‘intimately related ; but we must not forget that self-fertilization is a still closer method 
of in-breeding. Therefore if that be a cause of deterioration to the intercrossed, it 
. should, à fortiori, be so to the self-fertilized. But it cannot be; for if it were, the ratio 
should either remain constant, or else vary progressively in favour of the intercrossed, as 
the self-fertilized should deteriorate faster than the intercrossed. On the other hand, 
if it do not so vary, and the intercrossed be really deteriorated, there is but one inter- 
pretation, viz. that the self-fertilized have not deteriorated in the same ratio as the 
former. 
Such want of any correspondence between ratios of heights and successive generations 
occurred also with others of Mr. Darwin’s experiments; for thus was it with Petunia 
violacea and Nicotiana tabacum. The difference between the heights of the intercrossed 
and of the self-fertilized plants of the first named, arranged in a decreasing order, would 
be as follows :—4th, 5th, 2nd, 4th, 1st, 3rd years. In the last case, the ratio for the 
intercrossed to the self-fertilized was 100 : 131, where the difference has again increased, 
but is now in favour of the self-fertilized. 
12. The fertility of cultivated self-fertilized plants may increase in successive generations. 
Mr. Darwin gives some interesting illustrations of this fact (l: c. p. 112). Thus 
Eschscholtzia californica was self-sterile in Brazil, but in the first year's cultivation 
in England the ratio of the yield of seeds between the intercrossed and self-fertilized 
plants was 100: 15. Eight flowers on these self-fertilized plants (7. e. grandchildren of 
the plants which grew in Brazil) were again fertilized with pollen from the same 
plant, and produced five capsules with an average of 27:4 seeds; but in the previous 
year the average was only 12 seeds per capsule; hence the fertility of the self-fer- 
tilized plants was thus increased to more than double that of the first year. 
Dianthus Caryophyllus is naturally so strongly proterandrous, that Mr. Darwin was 
obliged often to use pollen from a different flower on the same plant for artificially self- 
fertilizing it. This species appeared to adapt itself to self-fertilization with great 
readiness by becoming homogamous. The proportion of seeds of parent plants inter- 
crossed and of self-fertilized plants was in the ratio of 100 : 92; and when the self- 
fertilized offspring was crossed by a new stock, the proportion of the latter to the again 
self-fertilized was in the ratio of 100 : 123. Similarly the third generation of the inter- 
crossed subsequently self-fertilized was in proportion to the fourth self-fertilized gene- 
ration as 100 : 125. 
The above results, taken from Mr. Darwin’s work, clearly show a steady increase of 
self-fertilizing power, which was acquired by the loss of dichogamy, the stamens and 
pistil maturing together. 
Looe Free from EV the self-fertilized planis may equal the intercrossed (1) as 
| seedlings, (2) when adult and planted in open ground. 
Bur. hist apps iom Ms Darwin's observations. E. 
= 210 Tuto m s 
