93 



INHIBITORY INFLUENCES 



Many influences which inhibit or retard vegetative growth, in so doing 

 call forth increased sporulation, in accordance with the second law of 

 Klebs ( 74) that the conditions favoring sporulation are always more or less 

 unfavorable for growth. Thus, two colonies of H. No. 1 on washed agar 

 were independently nearly devoid of conidia; but when they grew and ap- 

 proached each other, vegetative growth was retarded, and eventually in- 

 hibited, and each colony became dark in the region of inhibition, owing to 

 much-increased sporulation (Fig. 1). Colonies of many other species of 

 fungi affected H. No. 1 similarly under like circumstances, as did also dry- 

 ing out of the agar at the colony's edge. Similar changes in growth, and 

 consequently in colony-character, occur on almost any medium, prom- 

 inently on corn-meal agar, and they must be understood and reckoned 

 with if colony characters are to be used for descriptive purposes. 



Fig. 1 Illustrating inhibitory influence on 

 sporulation. Two colonies of H. No. 1, on washed 

 agar, showing dark bands, due to abundant sporu- 

 lation where the colonies approach each other. 

 Sporulation also somewhat increased near margins 

 of colonies, owing to drying. 



HUMIDITY OF MEDIA 



Rice was placed in tubes with water equal to twice the volume of the 

 rice, and with water equal to four times its volume, being then autoclaved 

 and inoculated with various Helminthosporiums. Notes at two weeks 

 show better characters of border, interstices, etc., in the wetter tubes, and 

 while with many strains sclerotia developed abundantly in the drier tubes 



