80 



species or strains of Helminthosporium. These are throughout referred to 

 by number rather than by name, partly for brevity and partly because 

 the species of many of the races had not been determined, while in some 

 cases the names were of more or less doubtful reliability. That the reader 

 may formulate his own judgment of these forms, introduced for comparison, 

 a complete list of them is given in the appendix (pages 181-184) together 

 with certain notes regarding them. 



VARIOUS AGARS AS MEDIA 



Corn-meal agar in Petri dishes. This medium, prepared after the di- 

 rections given by Shear and Stevens (104), was found to be admirably 

 suited to Helminthosporium and was the medium chiefly used. 



The fungus grew rapidly, the colony being at first nearly hyaline 

 both in the submerged and aerial parts, but when a diameter of about 2-3 

 cm. was attained the whole colony became much darker. Profusion of 

 conidia was the chief factor in giving the dark hue to a colony, the slight 

 darkening of the mycelium having little to do with it. The aerial mycelium 

 varied largely with change of conditions, sometimes being very scant 

 and at other times 5-6 mm. high, with windrow effects corresponding 

 with the zones. After the colony was about 3 cm. in diameter zonation 

 became quite pronounced, the zones corresponding approximately with 

 the growth of each day. At room-temperature the colony attained a 

 diameter of about 4.5 cm. in six days. Conidia-production was quite 

 uniform over the surface of the colony unless checked by some growth- 

 inhibiting cause, as drying, cold, or the antagonism of another colony 

 near by, when it was much increased, as evidenced to the eye by black 

 bands in such regions. By transmitted light the mycelium, and to some 

 extent the conidia at certain ages, had a distinctly greenish tinge. H. No. 1 

 could be distinguished from H. Nos. 5-8, which were paler and produced 

 fewer conidia. H. No. 6 approached nearer to H. No. 1 in these regards 

 than did the others. H. Nos. 3, 4 (see PI. IX), 6, 15-17, and 18 typically 

 developed more aerial white mycelium than did H. Nos. 1 and 14. H. No. 

 36 was of very distinct character owing to large development of aerial 

 mycelium (see PI. X). 



Corn-meal agar in Freudenreich flasks. The flasks, of about 100 c.c. 

 capacity, each received 50 c.c. of agar and were slanted. The large amount 

 of nutriment available and the sustained moisture gave noteworthy 

 characters. At 7 days, with H. No. 1, the surface of the slant was com- 



