147 



APPARENT REVERSIONS 



In several instances where colony color, aerial mycelium, or partial 

 sterility was the saltant character, small sectors of the colony were so 

 changed as to resemble closely the originals, and as far as tests were applied 

 could not be distinguished from them (PI. XXXII); in no case, however, 

 where true saltant character was proved by constancy through several trans- 

 fers did the whole stock revert; what appeared as reversion was limited to 

 occasional sectors of the colony, and in no case did such change occur in 

 the entire margin of a colony. 



SUPPOSITITIOUS CAUSES OF THE VARIANT SECTORS 



Several alternative suppositions other than that of saltation may be 

 briefly discussed as possible causes of the variant sectors. The mycelium 

 at a certain point may become weakened, or die, and the change in equilib- 

 rium resulting may cause the variant sector. Spores of another Helmin- 

 thosporium or of some other organism may fall into the colony from the air, 

 and the variant sector may represent merely a contamination. The in- 

 oculum used on a plate that shows saltation may have consisted of more 

 than one strain or elementary species of Helminthosporium. The first 

 supposition is open only to crude experimentation, while the second, if 

 valid, implies a wonderful Helminthosporium-richness in the air of my 

 laboratory as well as very faulty technique. Since saltation occurred after 

 the fungus, H. No. 1, had been transferred many times by lifting a small 

 bit of agar from the edge of a colony, the presumptive evidence that no 

 mixture then existed is very strong. The following experiments bearing 

 on these suggestions may, however, be worth recording. 



Wounding. A culture of H. No. 1 on corn-meal agar was allowed to 

 grow to a diameter of about 4 cm. Then by means of a hot iridium wire 

 the mycelium was killed at the points indicated in PI. XXIX, above. In 

 all cases the uninjured parts soon entirely outgrew the wounds, and the 

 whole colony presented an entire, normal outer border with no evidences of 

 saltation. In some instances a clear straight line extended from the point 

 of wounding nearly to the edge of the colony. Evidently disturbance 

 of equilibrium such as this did not cause saltation. 



Mixed planting. Acting on the 'knowledge that the saltants were 

 frequently slow-growing, and thinking that possibly ordinary transfers 

 might be mixtures of two or more races, of which the slower-growing one 

 ordinarily remained masked, M8, a well-characterized saltant, was planted 



