so nicely balanced, that
the face of nature remains uniform for long periods of time, though
assuredly the merest trifle would often give the victory to one organic
being over another. Nevertheless so profound is our ignorance, and so high
our presumption, that we marvel when we hear of the extinction of an
organic being; and as we do not see the cause, we invoke cataclysms to
desolate the world, or invent laws on the duration of the forms of life!

I am tempted to give one more instance showing how plants and animals, most
remote in the scale of nature, are bound together by a web of complex
relations. I shall hereafter have occasion to show that the exotic Lobelia
fulgens, in this part of England, is never visited by insects, and
consequently, from its peculiar structure, never can set a seed. Many of
our orchidaceous plants absolutely require the visits of moths to remove
their pollen-masses and thus to fertilise them. I have, also, reason to
believe that humble-bees are indispensable to the fertilisation of the
heartsease (Viola tricolor), for other bees do not visit this flower. From
experiments which I have lately tried, I have found that the visits of bees
are necessary for the fertilisation of some kinds of clover; but
humble-bees alone visit the red clover (Trifolium pratense), as other bees
cannot reach the nectar. Hence I have very little doubt, that if the {74}
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 degree on the
number of field-mice, which destroy their combs and nests; and Mr. H.
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 Mr. 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 in