1915] 



BURT THELEPHORACEAE OF NORTH AMERICA. IV 633 



extent that they can have little, if any, value for discrimin- 

 ating between species of Exohasidium. Into the formation of 

 such galls so many other factors besides the Exobasidium 

 hyphae enter that it is impossible to consider galls as homol- 

 ogous with the fructification of an ascomycete or that of a 

 toadstool, and they should not be used therefore in the way 

 these true fungous fructifications are used for affording in 

 their form specific characters. As a matter of fact, the layer 

 of basidia and conidia-bearing hyphae at the outside of the 

 gall comprise the whole fructification of the parasitic fungus ; 

 this layer alone is morphologous with a toadstool. The mere 

 form of the foreign substratum covered by the resupinate 

 fructification of Exobasidium should have no greater tax- 

 onomic weight than it has in the closely related genus 

 Corticium. 



We should now consider the distribution of Exobasidium 

 Vaccina as a parasite upon various genera and species of the 

 Ericaceae. Woronin limited his investigation of E. Vaccinii 

 to what he observed on Vaccinium vitis-idaea and left the 

 matter there for other investigators to go on with, if they 

 were so disposed. As the collections which are made on this 

 host nearly always show the fungus occurring in leaf spot galls 

 and leaf concavity galls, and since these forms of galls are 

 the only ones on this host common enough for distribution in 

 published exsiccati, the species Exobasidium Vaccinii seems 

 to have become altogether too closely associated with, and 

 limited in mycological practice to, merely the very com- 

 monest gall forms which are produced under stimulation by 

 E. Vaccinii. For example, Shear^ states, ''The typical 

 form of Exobasidium Vaccinii occurs on Vaccinium vitis- 

 idaea, producing hypertrophied spots on the leaves. No 

 record has been found of the occurrence of hypertrophied 

 shoots on this host similar to those found on cranberry plants. 

 Rostrup^i seems to have been the first to describe this form. 

 In 1883 he reported it as occurring on Oxycoccus palustris in 

 Denmark. ' ' 



1 Cranberry Diseases. U. S. Dept. Agr., Bur. PI. Ind., Bui. 110:36. 1907. 



