91 



wheat. The quantity of conidia produced, and correspondingly the black 

 color, bore a direct relation to the mass of the corn shoot. It is probable 

 that all of these autoclaved shoots are of equal, or nearly equal, nutritive 

 value for a given amount of material. 



Eleven other strains of Helminthosporium were tested in similar man- 

 ner, using wheat, oat, and barley shoots. No significant differences in 

 growth appeared, though, in most cases, at the end of the growth-period 

 there was a somewhat more profuse development of conidia on wheat than on 

 the two other cereals. 



ENVIRONMENTAL FACTORS WHICH INDUCE VARIATION 



Since classification of these fungi is necessarily based primarily on 

 morphology, and on growth characters as exhibited on various media, 

 it is important to know what, and how great, variations in these charac- 

 ters are induced by environmental changes. It is generally conceded that 

 culture characters to be comparable must be noted under similar condi- 

 tions. But how much latitude is permissible here; what difference in 

 environment may be regarded as negligible? Fungi are collected that have 

 grown under different conditions of nutrition, humidity, temperature, etc., 

 and specific descriptions are written, based on these collections. To 

 what extent are they trustworthy? The size and shape of the conidia and 

 septation are regarded as of the highest taxonomic value. The develop- 

 ment of sclerotia, of aerial mycelium, of mycelial clumps, of color, etc., 

 are often the only characters separating some types regarded as species. 

 Even the characters of the colony on the agar plate are considered im- 

 portant. It is with the hope of throwing some light upon this phase of 

 the subject that I record the following additional observations concerning 

 environmental factors which induce variation. More complete and ex- 

 haustive studies on these and kindred phenomena are needed. 



QUANTITY OF NUTRIMENT 



Petri dishes were respectively supplied with 12 c.c. and 30 c.c. of 

 60 corn-meal agar and inoculated with H. No. 1. Placed under the 

 same conditions, these dishes gave very different colony-characters. 

 The colonies on the plates containing the larger amount of agar were very 

 dense and black, and covered the agar-surface much more completely than 

 did the colonies on the plates containing less agar (PI. XIV). There was 

 also marked difference in the rate of linear growth, as is shown in the fol- 

 lowing table: 



