i6 



TECHNICAL BULLETIN 17 



Throughout the culture work, bizarre forms frequently appeared, 

 especially forked spores which were sometimes almost stellate. Seven 

 or eight such single spores were isolated and planted on agar slants. 

 In each case normal spores were produced and the bizarre type occurred 

 so rarely that it was quite impossible to isolate another single spore of 

 the same shape from the progeny. 



240 



O 20 4O 6O &O 



Lengfh of <spore<5 (microns) 



too 



/2O 



Fig. 3. Length of Spores of Helminthosporium sattivum Produced on Different 



Substrata at 24 C. 



The solid line represents spores produced on autoclaved ripe barley heads; the line with 

 short dashes, spores produced on potato dextrose agar; the line with alternate long and short 

 dashes, spores produced on fresh barley leaves in a moist chamber. 



TEMPERATURE RELATIONS 

 GROWTH OF FUNGUS ON POTATO DEXTROSE AGAR 



In determining the temperature relations of H. sativum, the first 

 problem studied was the growth of the fungus in pure culture. In all, 

 four series were run to determine the range of growth, the same gen- 

 eral method being used in each. Thirty cubic centimeters of potato 

 dextrose agar were poured into petri dishes 10 centimeters in diameter. 



