ii THE WEB OF LIFE 29 



evident, while it is also certain that insects are attracted 

 bv the colour, the scent, and the sweets. Xor can there 



J 



be any hesitation in drawing the inference that the flowers 

 which attracted insects with most success, and insects 

 which got most out of the flowers, would, ipso facto, 

 succeed best in life. 



No illustration of the web of life can be better than 

 the most familiar one, in which Darwin traced the links 

 of influence between cats and clover. If the possible 

 seeds in the flowers of the purple clover are to become 

 real seeds, they must be fertilised by the golden dust 

 or pollen from some adjacent clover plants. But as this 

 pollen is unconsciously carried from flower to flower by 

 the humble-bees, the proposition must be granted that 

 the more humble-bees, the better next year's clover crop. 

 The humble-bees, however, have their enemies in the 

 field-mice or voles, which lose no opportunity of destroy- 

 ing the combs ; so that the fewer field-mice, the more 

 humble-bees, and the better next year's clover crop. In 

 the neighbourhood of villages, however, it is well known 

 that the cats make as effective war on the field-mice as 

 the latter do on the bees. So that next year's crop of 

 purple clover is influenced by the number of humble- 

 bees, which varies with the number of field-mice, that is 

 to say, with the abundance of cats ; or, to go a step 

 farther, with the number of lonely ladies in the village. 

 It is reported that fertile seeds of the purple clover may 

 be formed in the absence of humble-bees, as for some 

 time in New Zealand ; in such cases there must be 

 either self-fertilisation or some other insect-visitor as 

 effective as the humble-bee. 



Not all insects, however, are welcome visitors to 

 plants ; there are unbidden guests who do harm. To 

 their visits, however, there are often obstacles. Stiff 

 hairs, impassably slippery or viscid stems, moats in 

 which the intruders drown, and other structural peculi- 

 arities, whose origin may have had no reference to insects, 

 often justify themselves by saving the plant. Even 

 more interesting, however, is the preservation of some 

 acacias and other shrubs by a bodyguard of ants, which, 



