H. WomiALD 55 



conidia readily when growing on semi-cylinders of sterilized potato in 

 Roux' tubes, the tufts of conidiophores being produced in more or less 

 continuous dark-grey parallel zones on the upper (thinner) half of the 

 potato. The apple " blossom-wilt" strains on the other hand have always 

 produced but a scanty crop of conidia when growing on potato, the 

 conidiophores developing in relatively few isolated tufts. 



The results afford evidence of the occurrence of l)iologic forms 

 within the species Monilia cinerea. That forms morphologically similar 

 but distinct in their biological relations with the host plant, occur 

 among tlie obligate parasites, the Uredineae and the Erysiphaceae, has 

 been fully proved (rt) and there is evidence that such forms occur also in 

 other groups; thus Grossenbacher and Duggar(H) conclude that Botri/o- 

 sphaeria ribis occurs as two forms, one parasitic on currant shoots, the 

 other apparently saprophytic only and they find that the two forms can 

 be distinguished by cultural characters. 



In Monilia cinerea the two strains which have behaved as biologic 

 forms can also be distinguished culturally and this suggests that bio- 

 chemical methods may throw some light on the physiological relations 

 of biologic forms in those fungi which, like Botryosphaeria ribis and 

 Monilia spp., allow of culture on artificially prepared media. Alsberg and 

 Black (3) working with several species of Penicillium pointed out in 1913 

 the desirability of applying biochemical methods in distinguishing the 

 lower forms of fungi which are not readily to be distinguished by their 

 morphological characters. 



In the case of the two strains of Monilia cinerea, the difference in 

 coloration suggested a differential action of some oxidising enzyme and 

 preliminary experiments have shown that one strain produces a sub- 

 stance of an enzymic nature, probably an oxidase, much more readily 

 than the other. These experiments are being continued for these two 

 strains and will be amplified by application to other strains. 



IV. CONTROL MEASURES. 



From the inoculation experiments recorded in this paper it is evident 

 that the form of Monilia cinerea. which occurs on the dead twigs of plum 

 trees is capable of infecting the flowers and causing a "brown rot" of 

 the fruit of the plum tree, and that such twigs if not removed serve as 

 sources of infection since they produce pulverulent pustules of conidia 

 by the time the trees are in flower. Although inoculation of the leaves 

 with pure cultures of the fungus have, up to the present, given negative 



