SELF-FERTILIZATION OF PLANTS. | 385 
Mimulus luteus, Table XIX., not crowded, . . . . . . . . 100: 109 
ap e ctowded i ahaha of wooed HEUO £4148 
Digitalie purpurea, Table XXIV., not crowded . . . . . . . 100: 94 
» » crowded, nis os dioi asw i 1008: DO 
So also when pairs of plants grown in pots are contrasted with similar pairs. in open 
ground very similar results occur :— 
Reseda lutea in open ground `, . . . . . . . .. 100 e Së 
M e EE EE EE Obi Ss 
KR. odorata in open;ground.. bis | uiuos awe: och ENEE 
0 s» mM SOBEL uo POGUE ROE qnt DOqu100vv ag 
Dianthus Caryophyllus in open g den: oles (RT ep (rr 260454 2120902 0:808 
o mpow ““pawli vd. EE . 100: 58* 
Lastly, a like difference resulted in the ae of plants of Petunia violacea when 
crossed with a new stock; for the ratio of the weights of what Mr. Darwin called the 
** Westerham-cerossed " to that of the self-fertilized was in pots as 100 : 22, but in open 
ground as 100 : 53, and to that of the normally intercrossed in pots as 100 : 101, while in 
open ground it was as 100 : 146 (Z. c. pp. 200, 201). 
Nicotiana tabacum illustrates the converse. This is a highly self-fertile plant. The 
ratio of the weight of seeds of the intercrossed to the self-fertilized was as 100 : 150, and 
that of their heights when young as 100: 189, but when adult as 100: 178. When, 
however, they were greatly crowded the ratio became one of equality, or 100 : 100. 
. Hence, whatever be the standard of measurement, the results appear to furnish the 
decided rule that self-fertilized plants regain their equivalency with or even an ascend- 
ancy over the intercrossed as soon as they are freed from competition ; consequently 
I do not see why Mr. Darwin should speak thus of Nicotiana :—“ It is a strange fact 
that the self-fertilised plants, which were subjected to very severe competition with the 
crossed, had on two occasions no advantage over them." I take the explanation to be 
this :—Tobacco is evidently a vigorous self-fertilizer, nevertheless crossing did some good ; 
but that good was not apparent, except under certain conditions, i. e. severe com- 
petition, when the introduction of some new constitutional elements had the opportunity 
of evincing their power, whereas the innate vigour of the self-fertilized Nicotiana com- 
pletely eclipsed it when free from competition. 
Finally, there are apparently but two alternatives to appeal to, in order to account for 
the fact that intercrossed plants are not so greatly superior to the self-fertilized when 
planted in open ground as when in competition in pots, viz. either the intercrossed plants 
become deteriorated on being planted in open ground, which would seem to be absurd, 
or else the self-fertilized must regain or acquire vigour in a relatively greater degree 
than do the intererossed, and thus would seem to evince what might be called a greater 
* elasticity " of growth than their intercrossed competitors. 
| 14. Some self-fertilized plants derived no benefit from a cross with another plant of the 
same stock, nor even from a cross with a plant of a distinct stock. 
. With regard to the first statement, it applies to plants long cultivated e coe eae | 
Dm o M DOM Darwin, see ‘ Cross and Self-fertilisation, p. 288.- eed 
