106 James G. Horsfall 



ner, tending in early stages to be almost invisible within an internal ring 

 about 3 or 4 millimeters from the edge. Th's gives the effect of a white 

 halo around the young thallus. The mycelium is a dark ivy green on 

 cornmeal agar. 



Culture 128 stands definitely alone, since it produces an abundance of 

 " white islands," which appear almost like minute somewhat feathery 

 white Clavarias in the plate. These structures, which are arranged in 

 concentric circles, are made up of closely compacted, large, barrel-shaped 

 hyphal cells that branch and fray out slightly at the distal ends. They 

 are from 2 to 4 millimeters high. The submerged mycelium has a velvety 

 olivaceous black appearance which fades to a medal bronz at the edge, 

 fringed with white. After the culture is two o: three weeks old, the black- 

 ish submerged mycelium tends to grow up and over the white islands, 

 dulling their appearance. 



Cultures 242 and 244 also appear greatly different from any of the others 

 and different from each other. Culture 242 is Hiathi gray uniformly over 

 the plate on oat agar. A few small white clumps, quite unlike those of 

 128, occur scattered over the plates. There is a small, sharply defined 

 central portion of lilac gray which changes to dawn gray on the margin. 

 Cornmeal agar separates out this strain because the mycelium here is a 

 dark grayish olive n the center, grading off to a light olive gray at the 

 edge instead of the usual dark ivy green. As the description indicates, 

 the mycelium of this form is much lighter than of any of the others. 



Culture 244 resembles 242 but it is somewhat darker and shows a white 

 fluffy center on all agars. It is dark olive gray around the edge on potato 

 agar, storm gray on oat agar, and deep olive on cornmeal agar. The sub- 

 merged mycelium is somewhat rhizomorphic on the last medium. 



On Coons' synthetic medium the fungus grows very slowly. That 

 medium is useless for differentitation. 



After having found these differences in culture, the next logical objective 

 was to determine whether differences in pathogenicity occurred, but a lack 

 of time prevented this from being carried to completion. 



Mutation. It seemed desirable also to determine if Helminthosporium 

 vagans mutates in culture. No sign of sector mutation was observed in any 

 of the strain work outlined previously until suddenly toward the end a single 

 " white island " similar to those described under culture 128 arose from 

 the otherwise blackish mass in one of the plates of oat agar of culture 271. 

 Upon transferring one of these carefully to another plate of oat agar, as 

 271 d, it developed almost precisely like culture 128 except possibly that 

 the submerged mycelium tended to be more nearly pink. White islands 

 developed profusely. Three subcultures of white islands failed to give 

 increased general whiteness of the culture. A hint of dark color in the 

 submerged mycelium remained. 



