DEFENCES OF PLANTS 349 



In discussing seed disposal, we have learned how 

 birds eat certain ripe fruits and scatter the contained 

 seeds. It is necessary to point out here that it would 

 be disastrous to the plants concerned if birds attacked 

 the fruits while unripe, and before the all-important 

 seeds were properly developed. We know that it is 

 only indiscreet children with a voracious appetite who 

 experiment with unripe fruits, and they usually suffer 

 the penalty of their indiscretion. Birds are wiser: sour, 

 hard, and unpalatable unripe fruits do not attract them ; 

 they wait until they are ripe, and when they are ripe 

 and sweet the seeds are ready for dispersal. While 

 the fruits are ripening, they are covered with a skin 

 which keeps water from without getting in, and the 

 water that is in from evaporating. Some fruits are 

 covered externally with " bloom," such as occurs on the 

 plum and grape. This bloom consists of wax, which is 

 antiseptic, and wards off fungi and bacteria. Every 

 vine cultivator knows how important it is to avoid dis- 

 turbing the bloom of the grape; at any point where it is 

 removed, fungi and bacteria may attack and induce rot. 



The manner in which certain Acacias are protected 

 by warrior-ants against the incursions of leaf-cutting 

 ants has already been described (p. 291). This is a 

 type of police duty which cannot be observed in Britain, 

 because here we have no leaf-cutting ants. But if we 

 examine the under surface of the leaves of such trees as 

 the Horse-Chestnut, Elm, or Lime, we may chance to 

 observe little groups of hairs in the forks of the veins, 

 which form a shelter for a number of very active mites. 

 These can be readily seen with the aid of a hand- 

 magnifier, such as any student of plants will find it 



