104 Secret of the Heather 



snail on a leaf and pecks off the pulsating horn, the 

 branch of the parasite, which is now full of larvae of 

 another generation, closes up automatically at its 

 base, so that there is no loss of the multitudinous 

 microscopic progeny. Now the investigators tell us 

 that if the Blackcap swallows the horn then and there, 

 nothing happens. The fluke-parasites are digested. 

 But if the bird gives the tidbit to its nestling, which 

 has a weaker digestion, then infection occurs and the 

 extraordinary life-cycle begins again. 



There are endless instances of the linking together 

 of lives apparently far out of touch with one another. 

 The malarial parasites pass from man to man by 

 aid of the mosquito ; the Trypanosome microbe, that 

 causes sleeping sickness, is disseminated by the tsetse 

 fly; bubonic plague is transferred from rat to man 

 by the intermediation of the rat-flea. Some of the 

 finest pearls appear to be formed in the pearl-oyster 

 as the sepulchre of the minute parasitic larvae of 

 flukes and tapeworms. 



One of the most striking biological facts in many 

 parts of Britain is the success of the heather. It grows 

 exuberantly on mountain and moorland where few 

 other flowering plants can make a living. There is 

 soil, but it is unready ; there is water, but it is apt to 

 be plrysiologically unavailable. How does the heather 

 flourish so well? The answer is that it has entered 

 into a very intimate partnership with a fungus, which 

 penetrates through and through the heather, from 

 root to stem, into every leaf, even into the flower and 

 its seed. What an individual could not do, a firm 



