344 Journal of Agricultural Research voi. vi, no. io 



Besides this test of different reactions of the medium, a series of 

 nutrition tests was conducted, a full nutrient agar, including carbon, 

 nitrogen, oxygen, hydrogen, potassium, phosphorus, magnesium, sulphur, 

 and iron, being used. With one exception each set of the media con- 

 tained one element less than the full nutrient culture; in other words, the 

 experiment was arranged as follows: (i) Check containing water agar, 

 (2) full nutrient, (3) full nutrient minus nitrogen, (4) full nutrient minus 

 potassium, (5) full nutrient minus phosphorus, (6) full nutrient minus 

 magnesium, (7) full nutrient minus sulphur, (8) full nutrient minus iron, 

 (9) full nutrient minus carbon, (10) full nutrient minus all minerals.. 

 Two plates of each kind of agar were inoculated with conidia and two 

 with mycelium from the same culture of S. atrovirens, and all were incu- 

 bated in the laboratory at room temperature. 



Examinations at the end of 15 and 20 days indicated that sporulation 

 occurred only on the plates from which sugar was omitted — that is, Nos. 

 I and 9 — the colonies on these plates being of a light color and spreading 

 character and from 1.5 to 2.5 cm. in diameter and that no sporulation 

 occurred on the plates from which sugar had been omitted, the mycelium 

 in these being dark and densely compacted and only 0.75 to 1.25 cm. in 

 diameter. 



This preliminary study of the reactions of media on 5. atrovirens indi- 

 cates that neutral or slightly acid reactions are more favorable for the 

 growth of this fungus; that the kind of medium determines the effect of 

 higher reactions on this organism as shown by the alkaline reactions of 

 beef agar compared with the same reactions of potato or the other agars; 

 that compounds in one kind of medium may be formed which are seem- 

 ingly toxic, whereas in a different kind of medium the same adjustment 

 produces no such inhibitory effects; and that the presence of 5 per cent 

 of cane sugar in a nutrient agar inhibited sporulation, but induced dark, 

 heavy, compact mycelial growth, while the absence of sugar caused 

 sporulation and a more spreading mycelial development. 



HISTOLOGY 



Studies were made to determine the relation of 5. atrovirens to the 

 potato. Both normal and affected material from the eye end of Irish 

 Cobbler, Green Mountain, and Minnesota Triumph tubers badly infected 

 normally and artificially was taken from the center and from the margin, 

 that from the latter with and without lenticels or eyes. This material 

 was embedded, sectioned, and stained according to ordinary cytological 

 methods. From these studies it was evident that the mycelium may 

 enter the tuber through the lenticels or between the lenticels through 

 the epidermis. 



After the fungus gains entrance the hyphae invariably form within the 

 cells, where they appear as a single branch of the mycelium; or they 



