Inter-Relations of Living Creatures 647 



mice than in the open country, for the cats hunt them down, 

 killing them though they do not eat them. Therefore, the more 

 cats the fewer field-mice, and the fewer field-mice the more 

 humble-bees, and the more humble-bees the better next year's 

 clover crop. It is easy to extend these "House-that-Jack-built" 

 stories. The more clover the richer the pasture for the cattle, and 

 the more roast beef for John Bull. The more kindly old ladies 

 there are in the village the more cats there will be, and this again 

 will favour the clover ! Thus cats and clover and cattle are linked 

 together. 



It has been stated that in some instances the purple clover 

 has seeded satisfactorily in the absence of humble-bees. This may 

 be due to the occurrence of self-pollination or to the visits of some 

 other insect which fills the humble-bee's role as pollinator. But 

 the main fact is well illustrated in the case of a country like New 

 Zealand. 



The Case of Red Clover 



When the farmers there first tried to cultivate the purple or 

 red clover, it failed to produce seeds, for there were no humble- 

 bees in the islands. Bees were introduced and they multiplied 

 apace ; the raising of clover-seed became commercially profitable. 

 A subsequent importation of American species of humble-bees 

 with longer tongues, readily able to reach far down into the floral 

 tube, was followed by further improvement in the yield of clover- 

 seed. In one province, in 1912, an area of 610 acres was sown 

 with red clover and yielded an average of 158 pounds to the acre. 



Distribution of Seeds 



Hardly less important than the pollination of flowers is the 

 distribution of seeds, and again we may begin with a classic case 

 from Darwin. When birds get their feet wet, clodlets of earth 

 often form on them, and these may include the seeds of plants, 

 and, besides these, small animals or their larval stages. When the 



