442 Prof. H. Marshall Ward. The Relations between 



to say anything about their nutrition beyond the general statement 

 that they must have established such close temporary relations with 

 the living cells of the host that their protoplasm and that of the host 

 can go on absorbing nutriment from the same sources. This would 

 seem to be proved by the curious phenomena of hypertrophy which 

 they induce, e.g., the young shoots of Euphorbia cyparissias are entirely 

 altered in habit by the Mci&ium of Uromyces Pisi, and the well-known 

 " witches' brooms " of the silver fir,* for although the changes induced 



Fig. 16. A specimen of " witches' broom," on the silver fir, caused by the stimu- 

 lating action of the Uredinous fungus Mci&ium elatinum, the mycelium of 

 which lives perennially in the cortex, &c, of the fir, and causes some of its 

 buds to grow up into erect shoots of totally different habit from the normal 

 branches. The blister-like iEcidia are visible on the leaves at a and b (Hartig) . 



imply that the cells are carrying out their functions in a modified 

 manner, still they grow, divide, and evidently discharge their main 

 duties much as usual. Consequently it is impossible to believe that 

 any individual cell suffers much direct injury, and at least the proto- 

 plasm and nucleus, and even the chlorophyll corpuscles, &c, may re- 

 symbiotic connexion with the cells, and for some time merely taxes them, as it were, 

 rather than injures them directly. Of course, there is ultimate injury, and even 

 death, brought about in these cases ; but how much this differs in different cases is 

 evident from comparison of other fungi, like Peronospora parasitica, Podosphcera 

 Castagnei, with Uredines such as Hemileia vastatrix, Melampsora G-oepper- 

 tiana, &c. 



* Such hypertrophies are not confined to the Uredinese, however : cf., de Bary, 

 * Morph. and Biol, of tfungi,' 368—369, and Zopf (Schenk, ' Handb.,' vol. 4, 1889 

 pp. 504—507). 



