Some of the self-fertilised plants of the sixth generation were
intercrossed, as were some in the eighth generation; and the seedlings
from these crosses were grown in competition with self-fertilised plants
of the two corresponding generations. In the first trial the
intercrossed plants were less fertile than the self-fertilised, and less
tall in the ratio of 100 to 110. In the second trial, the intercrossed
plants were more fertile than the self-fertilised in the ratio of 100 to
73, and taller in the ratio of 100 to 92. Notwithstanding that the
self-fertilised plants in the second trial were the product of two
additional generations of self-fertilisation, I cannot understand this
discordance in the results of the two analogous experiments.
The most important of all the experiments on Mimulus are those in which
flowers on plants of the eighth self-fertilised generation were again
self-fertilised; other flowers on distinct plants of the same lot were
intercrossed; and others were crossed with a new stock of plants from
Chelsea. The Chelsea-crossed seedlings were to the intercrossed in
height as 100 to 56, and in fertility as 100 to 4; and they were to the
self-fertilised plants, in height as 100 to 52, and in fertility as 100
to 3. These Chelsea-crossed plants were also much more hardy than the
plants of the other two lots; so that altogether the gain from the cross
with a fresh stock was wonderfully great.
Pages:
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135