266 TIMBER AND SOME OF ITS DISEASES [chap 



by this parasite to the weeds which it infests, and at 

 any rate we aie not called upon to deplore its 

 destructive action on these garden pests : it is 

 sufficient to point out that the influence of the 

 mycelium is to shorten the lives of the leaves, and to 

 rob the plant of food material in the way referred to 

 generally in the last chapter. 



What we are here more directly interested in is the 

 following. A few years ago Wolff showed that if the 

 spores from the JEctdia of Peridermticm Pint 

 (van acicold) are sown on the leaf of Senecio, the 

 germinal hyph^ which grow out from the spores enter 

 the stomata of the Senecw leaf, and there develop tnto 

 the fimgns called Coleosporittm Sencaonis, In other 

 words, the fungus growing in the leaves of the pine, 

 and that parasitic on the leaves of the groundsel and 

 its allies, aie one and the same : it spends part of its 

 life on the tree and the other part on the herb. 



If I left the matter stated only in this bald manner 

 it is probable that few of my readers would believe 

 the wonder. But, as a matter of fact, this pheno- 

 menon, on the one hand, is by no means a solitary 

 instance, for we know many of these fungi which 

 require two host-plants in order to complete their 

 life-history ; and, on the other hand, several observers 

 of the highest rank have repeated Wolff 'b experiment 



