138 THE BALANCE OF NATURE. 



begun to find out that the fiuiners were right 

 after all, and that the barberr^'-bush does really 

 destroy the corn in its neighborhood. For smut 

 or rust, that very destructive enemy of the wheat- 

 plant, is really a small fungus or vegetable para- 

 site, which passes through various stages, some- 

 thing like those of the caterpillar, the chrysalis, 

 and the butterfly in the insect world. Now, the 

 first or infantile stage of smut is passed in tlie 

 barberry -leaves, from which the spores or tiny 

 seeds of the fungus finally migrate, being blown 

 by the wind among the nearest wheat-fields. 

 But, if there were no barberry -bushes, there would 

 be no leaves on which to nurse the young smut- 

 fungi, and so the disease would soon be extermi- 

 nated altogether. If we were to root up all the 

 barberries in America, we should stamp out the 

 smut with it. Farmers are beginning to be alive 

 to this fact at present, and the poor barberries are 

 being grubbed up with exemplary diligence out of 

 all the woodlands. 



Inter-relations of this sort are verv common 

 among cultivated crops, though it is only in quite 

 recent years that the attention of naturalists has 

 been fairly directed to them. There seems no good 

 reason at first sight, for instance, why plum-trees 

 should not be grown in the orchard of a hop- 

 farmer ; but Kentish experience has long shown 

 the English farmer that hops are specially affected 



