STRUGGLE FOR EXISTENCE 1479 



clover (Trifolium repens) yielded 2,290 seeds, but 

 20 other heads protected from bees produced not 

 one. Again, 100 heads of red clover (T. pratense) 

 produced 2,700 seeds, but the same number of pro- 

 tected heads produced not a single seed. Humble- 

 bees alone visit red clover, as other bees can not 

 reach the nectar. It has been suggested that moths 

 may fertilize 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 humblebees became extinct or very 

 rare in England, the heart's-ease and red clover 

 would become very rare, or wholly disappear. The 

 number of humblebees 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 

 humblebees, 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 New- 

 man says, "Near villages and small towns I have 

 found the nests of humblebees 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 interven- 

 tion first of mice and then of bees, the frequency of 

 certain flowers in that district! 



The dependency of one organic being on another, 

 as of a parasite on its prey, lies generally between 



