I 9 4 RESEARCHES ON FUNGI 



position of the hymenium in Exobasidium may be decided not by 

 the stimulus of gravity but by the structure of the leaf of the host. 

 The gall serves to increase the amount of surface which the 

 hymenium can occupy and thus favours the production of a larger 

 number of spores. 



A Brazilian species of Exobasidium, E. Leucothoes, according to 

 Hennings, 1 causes galls on the twigs of Leucothoe, which resemble 

 witches' brooms or the branches of a Clavaria. Thus a special 

 new surface area of considerable extent comes into existence upon 

 the host upon which the hymenium can be deployed. We thus 

 see that here, as in E. Vaccinii, the parasite moulds its host, in 

 much the same manner as do many insects, into forms which are 

 favourable to its own existence. 



1 P. Hennings, in Engler u. Prantl, he. cit. 



