137 



Though infection can be determined with certainty, I have as yet no 

 means of accurately measuring rotting power, or of determining whether 

 differences noted in rotting are due to environment, host, or fungus. 

 It seams clear, however, that H. No. 29 is capable of causing only local 

 spotting; and that the other numbers, perhaps even the saltants, vary 

 somewhat among themselves in rotting capacity, most of them causing rot- 

 ting to some extent under favoring conditions. 



The fact that so many and diverse races of Helminthosporium are 

 able to cause rot of wheat, led me to test the ability of Alternaria to para- 

 sitize wheat seedlings. An Alternaria, found commonly on wheat seed, was 

 isolated and inoculation made in rag doll on wheat seedlings. At 24 hours 

 many wheat cells showed diseased spots, being in every way like those 

 described on pages 128, 129, including the swollen middle and inner lamellae, 

 browning of the cell-contents, and formation of the "callus" and penetrating 

 mycelium. The Alternaria mycelium crossing several middle lamellae, 

 usually produced an appressorium and penetration at each middle lamella. 

 The Alternaria mycelium was also seen to enter the wheat-cells, killing a 

 few of them, but in no instance was this fungus observed to cause rotting 

 or to produce a spot large enough to be visible to the naked eye. It was 

 seen, however, to penetrate the cells of the root cortex quite extensively, 

 causing a slight browning. Sterigmatocystis, Penicillium, and several 

 other fungi supposed to be mere saprophytes, were treated in simitar 

 manner, but produced none of the phenomena of infection. 



SUSCEPTIBILITY OF VARIOUS HOSTS TO INFECTION 



Tests in rag doll with H. No. 1 



Corn. Three seedlings showed no infection at 2 days, though conidia 

 were present and had germinated. At 6 days all three plants were in- 

 fected, the infection being confined to one or two cells, though the myce- 

 lium was clearly evident in these. Pammel, King, and Bakke (90) report 

 negative results regarding infection trials of H. sativum on corn, but their 

 tests were limited to leaves. 



Barley. At two days one plant was slightly infected, showing sev- 

 eral lesions. In these the mycelium was abundant within the cells. Eight 

 were not infected. At 6 days the infection showed no further progress. 



Rye. At two days three plants were infected; six not infected. At 

 6 days the infection showed no progress. The mycelium was observed with- 

 in the cells and infection phenomena were as on wheat. 



