92 



GROWTH IN DIAMETER OF COLONIES (MILLIMETERS) 



On 12 c.c. of agar 

 pi. 1, 22 

 pi. 2, 25 

 pi. 3, 29 

 pi. 4, 32 

 pi. 5, 25 

 pi. 6, 29 

 pi. 7, 27 



Totals, 189 

 Av. per pi., 

 27 mm. 



It appears that at 4 days the colonies on the deep agar grew more 

 than 32% faster than those on the plates with less agar; at 11 days, more 

 than 28% faster, the colonies being at the same time more dense. A 

 repetition of the test with 16 plates gave at 9 days a growth-average of 

 50 mm. on the shallow agar and of 74 mm. on the deep agar an increase 

 of 48% in rate. 



Since it was deemed possible that the differences here noted might 

 be due to differences in humidity, the depths of several plates were care- 

 fully measured and sufficient agar poured into each to make the air-space 

 above the agar in all cases equal, although, since half of the plates were 

 shallow and half of them deep, there was a great difference in the depth 

 of agar used, which averaged in the deep plates about 11 mm. and in the 

 shallow plates about 3 mm. The results of this test were almost identical 

 with those recorded above. The differences noted, therefore, could hardly 

 have been due to differences in humidity, but rather to the amount of 

 nutriment available. The graphs of conidial length given in Fig. E show a 

 larger predominance of short conidia on the deep agar, indicating the contin- 

 uance of conidia-formation for a longer period of time. For this reason 

 the mean length is much lowered and the coefficient of variability on the 

 deeper agars is much higher than on the plates with less agar. 



These results on deep agar are in entire agreement with those already 

 given concerning corn shoots (page 90), to the effect that quantity of nutri- 

 ment available may influence the growth-characters very markedly, often 

 as distinctly as does the quality of the food available. The dilution ex- 

 periments with green-wheat agar and corn-meal agar (pages 83 and 84) tend 

 toward the same conclusion, though other factors also appear in those cases. 



