STRUGGLE FOR EXISTENCE 87 



then cattle and horses would become feral, and this would 

 certainly greatly alter (as indeed I have observeu in parts 

 of South America) the vegetation: this again would largely 

 affect the insects; and this, as we have just seen in Stafford- 

 shire, the insectivorous birds, and so onwards in ever-in- 

 creasing circles of complexity. Not that under nature the 

 relations will ever be as simple as this. Battle within battle 

 must be continually recurring with varying success; and yet 

 in the long-run the forces are so nicely balanced, that the 

 face of nature remains for long periods of time uniform, 

 though assuredly the merest trifle would 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, 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 is never visited in 

 my garden by insects, and consequently, from its peculiar 

 structure, never sets a seed. Nearly all our orchidaceous 

 plants absolutely require the visits of insects to remove their 

 pollen-masses and thus to fertilise them. I find from experi- 

 ments that humble-bees are almost indispensable to the fer- 

 tilisation of the heartsease (Viola tricolor), for other bees 

 do not visit this flower. I have also found that the visits of 

 bees are necessary for the fertilisation of some kinds of 

 clover; for instance, 20 heads of Dutch 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 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 

 suflkient to depress the wing petals. Hence we may infer 

 as highly probable that, if the whole genus of humble-bees 



