BUTLER. 279 



is the same copious production of conidia on chlorotic streaks 

 on the leaves, the same absence of oospores, and the leaves do 

 not split longitudinally, as they do in most cases of infection by 

 S. graminicola. But the conidia differ so considerably in size 

 and shape that it is not safe, in the absence of oospores, to consider 

 the two forms to be merely varieties of the one species. For the 

 present, therefore, it appears best to preserve the specific rank of 

 the maize Sclerospora, as S. Maydis (Rac). 



The life-history of the cereal downy mildews, which all belong 

 to the present genus, is the most obscure amongst the Peronos- 

 poracece. Repeated attempts to germinate the oospore have 

 failed. The conidia appear to be short-lived. The symptoms 

 of the disease point to general infection of the plant, similar to 

 what is known in the grain smuts, but whether this infection occurs 

 subsequent to germination or results from mycelium already present 

 in the grain at the time of sowing, is not known. Peglion 1 found 

 the mycelium in the pericarp of wheat grains from deformed ears 

 of plants attacked by S. macrospora and was able to trace its growth 

 in plants developed from these seeds, but only when the grain was 

 sown before it ripened fully. I have grown a considerable number 

 of plants of Pennisetum from grain gathered from partly deformed 

 ears, but without getting a single case of the disease. Kulkarni 

 reports similar experiments with both Pennisetum and Sorghum. 

 and neither he nor I have been able to find the mycelium in such 

 grains. Further, I found several typical cases of the green ear 

 disease of Pennisetum in a plot sown with grain heated by immersion 

 in hot water to 65° C, for five minutes, a treatment known to be 

 sufficient to kill the mycelium, and even the spores, of the grain 

 smuts. It is probable, therefore, and Peglion himself is of the 

 same opinion, that infection normally takes place after germination. 

 This is most likely to occur through germination of oospores produced 

 in the previous crop. 



1 Peglion, V. Ueber die Biologie der Sclerospora, eines Parasiten tier Gramineen. Cen- 

 tralblatt fur Bakteriologie, 2nd Ab. XXVIII, 1910, p. 580. 



