36 



MASS. EXPERIMENT STATION BULLETIN 183. 



week after the colony is made. If one has to wait two or three weeks or 

 longer for a character to appear, the long waiting makes diagnosis tedious, 

 and one of the principal purposes of this method of diagnosis is defeated. 

 The more important characters for distinguishing these two species are 

 italicized. Many minor distinguishing characters are not mentioned. 



Potato Agar. 



C. scoparium. 

 Growth only moderately good. 

 Starts with abundant, perfectly white, 

 raised, aerial mycelium, but soon falls 

 flat at the center, which becomes cov- 

 ered with spores after two or three 

 days. Always more or less aerial 

 mycelium out toward the margin, which 

 is rather coarse and tow-like. Not a 

 decided color in reverse during the first 

 week, but a dilute cream color to buff. 

 At the end of the second week it turns 

 to avellaneous or wood brown, and 

 after three weeks still darker, Rood's 

 brown. Margin of colony crenulafe or 

 wavy. 



C. parvum. 

 Only moderately good growth. My- 

 celium finer and denser than C. sco- 

 parium, perfectly white. Spores pro- 

 duced in great abundance. The edge 

 entirely throughout its growth remains 

 very even and forms a perfectly round 

 colony. Practically no color — possibly 

 a very faint buff — develops in reverse 

 even after three weeks' growth. 



Sugar Potato Ag.^r. 



C. scoparium. 

 Very rank growth, abundance of 

 spores, entire plate covered in two 

 weeks. Dense opaque color appears in 

 reverse after three days; vinaceous 

 purple to hcematite red at the edge, dark- 

 ening to russet or chocolate at the center. 

 At the end of a week a large central area 

 appears almost black, but examined more 

 closely shows various shades of reddish 

 brown, chestnut and bay. Entire reverse 

 opaque after two weeks. The brown 

 color is due to the extremely abundant 

 production of sclerotia and chlamy- 

 dospores on this agar. 



C. parvum. 

 Rank, white growth of a very much 

 finer texture than C. scoparium. Abun- 

 dant production of spores. Color in 

 reverse, ivhite, or at most, only cream 

 color at end of one week. This is one of 

 the best diagnostic characters. At the 

 end of two weeks it has passed through 

 gray and drab gray to a clear wood 

 brown, with minute patches of army 

 brown here and there which show 

 chlamydospores under microscope. The 

 red-brown colors of C. scoparium never 

 appear. 



Gelatin. 



C. scoparium, 

 very poor, consisting 



Growth very poor, consisting of a 

 thin covering of coarse radiating hj-phae. 

 Very few spores. Stops growing after 

 about ten days. Gelatin turned to a 

 watery liquid which at the end of a 

 week is orange rufous, but gradually 

 turns darker to Sanford's brown. Lique- 

 faction extends some distance beyond 

 the margin of the colony. 



C. parvum. 

 very scanty, 



Growth very scanty, so much so 

 that it is necessary to look at the plate 

 against a black background to see it 

 at all during first week. Gelatin lique- 

 fied. No color at first, but becomes 

 dilute old gold by end of second week. 

 This medium is hardly suitable for dis- 

 tinguishing the two. 



