1907] 



STEVENS— CHRYSANTHEMUM RAY BLIGHT 



251 



concentric zones formed with great regularity, five dense zones 

 and six lesser zones being formed in a period of eleven days. In 

 the older central portion pycnidia began to form at the end of about 

 eight days, though often later. Pycnidial formation proceeds from 

 the central zones to the younger zones, the pycnidia being most 

 numerous in the denser zones, although they are by no means lack- 

 ing in the lesser zones. 



Upon hoiled ric€j in test tubes^ the fungus grew luxuriantly. As 

 the threads first invaded the rice there was 

 developed a salmon color, which later turned 

 to black. 



Upon hoiled corny in test tubes, the 

 mycehum developed well, became black, 

 and pycnidia were present in abundance 

 at the end of eleven days. 



The 



most striking 



features noted in 



these nutrition studies were the influence 

 of starch and glucose in agar or the starch 

 of the rice or corn media in causing the 

 development of an intense black coloration 

 in the mycelium; and the unfavorable in- 

 fluence of peptone, beef, and gelatin as 

 evidenced by distorted mycelium and the 

 failure to develop pycnidia. 



The jormaiion of zones is the most char- 

 acteristic feature of growth of this fungus 

 upon clear^ solid media {fig. ii). Reference 

 has constantly been made to this feature. _ rapidly growing hyphae. 

 The lesser zone, the zone which immediately 



surrounds the point of inoculation, is due to the mycelium growing 

 out rapidly in every direction from the point of inoculation. As 

 each individual thread becomes more and more distant from the 

 center and has made more and more branches, the threads begin to 

 crowd each other much more closely until, if conditions be proper, 

 a time is reached when apparently the crowding becomes so great 

 that further grow^th in length is inhibited. There then occurs a 

 development of aerial hvohae and a thickening and darkening of the 



Fig. 10. — Tips of young 



