Again, 100 heads of red clover (T. pratense) produced
2,700 seeds, but the same number of protected heads produced not a single
seed. Humble bees alone visit red clover, as other bees cannot reach the
nectar. It has been suggested that moths may fertilise the clovers; but I
doubt whether they could do so in the case of the red clover, from their
weight not being sufficient to depress the wing petals. Hence we may infer
as highly probable that, if the whole genus of humble-bees became extinct
or very rare in England, the heartsease and red clover would become very
rare, or wholly disappear. The number of humble-bees in any district
depends in a great measure upon the number of field-mice, which destroy
their combs and nests; and Colonel Newman, who has long attended to the
habits of humble-bees, believes that "more than two-thirds of them are thus
destroyed all over England." Now the number of mice is largely dependent,
as every one knows, on the number of cats; and Colonel Newman says, "Near
villages and small towns I have found the nests of humble-bees more
numerous than elsewhere, which I attribute to the number of cats that
destroy the mice." Hence it is quite credible that the presence of a
feline animal in large numbers in a district might determine, through the
intervention first of mice and then of bees, the frequency of certain
flowers in that district!
In the case of every species, many different checks, acting at different
periods of life, and during different seasons or years, probably come into
play; some one check or some few being generally the most potent, but all
will concur in determining the average number, or even the existence of the
species.
Pages:
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140