114 TECHNICAL BULLETIN 4. 



the entire center or wrinkled part of the growth. The convoluted gray growth on 

 onion agar is perhaps the best diagnostic cultural character of the species. It has 

 been very constant in the many series of cultures which the writer has made with 

 this agar. After a few weeks the color in reverse becomes darker, reaching cinna- 

 mon brown in about five weeks. 



Sugar Potato Agar. 



Prepared as potato agar with the addition of 3 per cent of saccharose. Growth 

 is coarser in texture, more luxuriant and spreads more rapidly than on potato 

 agar. The aerial mycelium is not snow white, but early assumes a cream color 

 changing to cartridge buff after a few weeks. 



Effect of Concentration of Sugar on Growth of the Mycelium in Culture.. — 

 In the series of cultures on different media it was observed that the best 

 growth occurred on media containing considerable sugar, viz., Czapek's, 

 sugar potato and onion agar. This led the writer to suspect that sugar is 

 the essential element of nutrition both in culture media and on the host 

 itself, since the onion contains a high percentage of saccharose. In order 

 to determine the effect of sugar on the development of the organism, 

 Czapek's synthetic agar was prepared first without any sugar and next 

 with .5, 1, 2, 3, 5, 7 and 10 per cent of cane sugar. Five tubes of each 

 were inoculated at the same time and accurate notes taken each day. No 

 growth whatever occurred where no sugar was included. At the end of 

 three weeks there was very little difference in the diameter of the growths 

 on all the othei concentrations, but those on the higher concentrates were 

 a little more dense. The most apparent difference was in the color which 

 was imparted to the agar. In the . 5 per cent the culture was pure white 

 in reverse, while in the 10 per cent it was bright yellow. The other con- 

 centrates formed a perfectlj^ graded series between the two. The only 

 other difference noticed was a wiinkling of the surface of the growth in 

 some of the higher concentrates, and its entire absence from the cultures 

 of low sugar content. Certain conclusions seem warranted from this 

 experiment: (1) agar and inorganic salts alone do not furnish food for 

 growth; (2) the yellow color in the agar is due to some reaction with the 

 sugar; (3) the amount of groAvth (at least for three weeks) does not depend 

 on the amount of sugar present. Any one of the concentrates apparently 

 contained more than the maximum amount which the organism could 

 utilize. 



Substitution of Starch for Sugar. — In order to see whether the fungus 

 can utilize starch as a source of carbon, agar tubes were prepared identical 

 with Czapek's except for the substitution of soluble starch for saccharose. 

 A scanty growth occurred, but even after four weeks it had not attained a 

 diameter of 1 cm, and was very thin. Apparently, then, Urocystis can 

 utilize starch, but it is a very poor source of carbon. 



Soil Decoction Agar. 



Prepared by adding 2 per cent of agar to the soil decoction described above. 

 Growth was much less vigorous than on potato agar, and thin, but, on the other 



