1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 243 



Alternaria Citri Pierce. The cultural characters were not greatly 

 different, and the differences might well be interpreted as due to 

 the development of the fungus in a different environment. 



The spores of this Alternaria were consistently larger than those 

 from the culture of Alternaria Citri and yet the spore sizes of 

 both fell inside the limits prescribed by Pierce ( ? 02). A brief 

 comparison of the cultural characteristics of these two cultures 

 is given below and checked against the description by Pierce 



Spores. — The spores of the culture of A. Citri used were few in 

 number, and within the limits of 11-22 X 5.5-8.2 fx in a large number 

 of spores measured from various transfers. The spores exhibited 1-3 

 cross-walls, were light brown to dark brown, and in chains of 2 or 

 3. Germination was slow and the percentage of germination low. 

 The spores of Alternaria sp. were numerous and within the limits 

 23.3-35.7 X 8.2-13.2 [x. There were 1-7 cells divided off by longi- 

 tudinal as well as transverse walls, dark brown in color, and when 

 viewed in position in a Petri dish culture were seen to be in long branch- 

 ing chains. These spores germinated readily in 24 hours at Ph 3.0, 

 in 31 hours at Ph 2.7, and a few germinated at Ph 2.5. Pierce ('02) 

 gave the dimensions of spores as 10-22 X 8-15 to 25-40 X 15-25 (x, 

 3-6-septate. dark olive-brown, and 3-6-catenulate. These limits 

 would include both of the cultures used by the writer. 



Cultural characteristics. — A. Citri was a slow-growing species, not 

 doing well on inorganic nitrogen sources. On solid media (agar) it 

 formed a nearly circular colony showing marked radiate growth 

 with little or no aerial mycelium. The colony appeared black on 

 both sides except for the white, growing edge. In liquid media 

 the mat was white, growing in the solution. Alternaria sp. was a 

 profuse grower as compared with the A. Citri culture used. On agar 

 plates the culture was black when viewed on the reverse side, 

 with a narrow white edge, and it was decidedly zonate. The upper 

 surface was covered with white to gray aerial mycelium. Under such 

 conditions spores were sometimes produced profusely and at other 

 times almost not at all. The amount of aerial growth was likewise 

 irregular, weather conditions, i. e., temperature and humidity, ap- 

 parently being the deciding factors. Older cultures produced fewer 

 spores, indicating that the failure of the A. Citri culture might be due 

 to too long a period in culture. In liquid media the mat tended to 

 become pinkish, where there was a good supply of carbohydrate, and 

 later dark. The mat grew in the solution. 



Pathogenicity. — When inoculated into ripe, sterile lemons A. Citri 

 produced, in some instances, a small rotted area limited to the rag, 

 but in some of these rotted areas there were signs of contamination. 

 On inoculation, by cutting into the rind and inserting mycelium, 

 Alternaria sp. produced a definite rot limited largely to the rag and 



