Il6 DISEASE IN PLANTS. 



beyond the natural barriers of the tissues, and so 

 puts a cordon all round the territory and seizes the 

 multitudes of food-stuffs at the frontiers. The end 

 result is similar in both cases, but the methods of 

 warfare differ. 



Many fungi, however, though they make their 

 presence noticeable by conspicuous signs, cannot 

 be said to do much damage to the individual 

 plant attacked. The extraordinary malformations 

 induced by parasites like Exoascus, which live in 

 the ends of twigs of trees and stimulate the buds 

 to put out dense tufts of shoots, again densely 

 branched Witches' brooms are a case in point. 

 Also the curious distortions of nettle stems swollen 

 and curved by yEcidzuni, of maize stems and leaves 

 attacked by Ustilago, and of the inflorescences of 

 Capsella by Cystopus, etc., are not individually very 

 destructive; it is the cumulative effects of numerous 

 attacks, or of large epidemics, which tell in the end. 



Some very curious effects are due to fungi such 

 as Vadium elatinum, which, living in the cortex 

 of firs, stimulate buds to put out shoots with erect 

 habit, and with leaves which are radially disposed^ 

 annually cast, and differently shaped from the 

 normal characters quite foreign to the species of 

 fir in its natural condition. 



Equally strange are the shoots of Euphorbia 

 infested with the aecidia of Uromyces, those of bil- 

 berries affected with Calyptospora, etc. In all these 

 cases we must assume a condition of toleration, so 

 to speak, on the part of the host, which adapts 

 itself to the altered circumstances by marked 



