W. MCRAE 235 



and from the living part of which a new shoot had developed in the early part 

 of the growing season. The leaves of the living shoot were wilting and falling 

 off. Hyphse of P}iijtoj)liOiora were found in the living tissue of the parent 

 branch, and in the new shoot at the places indicated. They were not found in 

 the shoot beyond these places, neither were they in or on the leaves. Figure 2 

 is a similar case, but three shoots had developed and become wilted. The 

 hyphaG were found as in the former example, but had extended backwards in 

 the main axis to a distance of 7 centimetres. The search for hyphte was 

 carried farther back than in the former case, and none were found in the 

 branch system nearer the main stem. Except for this one end-branch 

 that had died back and the three wilted shoots, all the subsidiary 

 branches springing from the one that left the main branch were free 

 from the fungus. Parts of the infected areas just beyond the limit of the 

 partial die-back when incnbated produced sj)orangia of Phylophlliom in both 

 examples. Such cases are found when the young leaves have flushed and 

 the wilting shoots are easily seen. Marked infected shoots have not been 

 seen to do this in the ensuing season, as in every case noted another fungus, 

 usually Botrijodiplodia thedbromcB Pat., has infected the dead branch and 

 carried on a die-back beyond the limits of the Phylophthora. This happens 

 in nature in a great many, probably the majority of cases in which 

 Phf/tophfJiora has begun the die-back, and it seems that only a comparatively 

 small number of partially died-back branches can actually reproduce the 

 disease in the succeeding season. The fungus has not actually been found 

 in this portion to come out to the surface and produce sporangia in nature, 

 but there is little doubt that it does so when the air becomes very moist at the 

 beginning of the monsoon. A similar instance of perennial mycelium has 

 been given by Butler and Kulkarnii where the mycelium of P. colocasice may 

 survive the dry weather and start renewed growth in the succeeding wet 

 season. Melhus^ has given a list of species of Peronosporacece that have been 

 reported to have perennial mycelium, and among them, besides the one just 

 mentioned, are two species of Phjtophthora, P. infestims and P. cactorum. 

 During the monsoon a similar thing happens, but, instead of wilting, the 

 leaves fall off. Figure 3 is a diagrammatic representation of a branch system 

 that was examined in the middle of July. The lowest side-branch which was 

 a new one had its terminal bud infected in April, and was now dead almost 



1 Butler, E. J., aad Kulkami. G. S. "Studies iu Pero>iosporace(e," Mem. Dent. Agric, 

 India, Bot. Serias, V, pp. 233— 2G1, 1913. 



2 Mclhus, I. E. " Poronnial Mycelium in species of Peronosporacece related to Phylophthora 

 infedans.'" Jowrn. Agric. Res., V, p. 67, 1915. 



2 



