1 8 THE COTTON PLANT IN EGYPT CHAP. 



in the United States. It is practically omnivorous, and is 

 the only damping-off fungus which seriously attacks cotton 

 seedlings in the Egyptian fields. The organism is an 

 extremely simple one, probably a degenerate Basidio- 

 mycete, but devoid of any spore-forms. A resting-stage is 

 produced by free branching of hyphae into clusters of short 

 swollen cells, which turn brown, forming irregular hard 

 black spots on the mycelium. Such resting-cell forma- 

 tion precedes the staling or exhaustion of an ample food 

 supply. The mycelium containing these cell-clusters has 

 been kept over calcium chloride for nearly two years, and 

 sent out abundant hyphae when moistened at the end of 

 the period. The hyphae are all equivalent, in the absence 

 of any sexual process, and are diagnosed by a curious 

 septum which is formed in each lateral branch immediately 

 above the point of origin . 



When a cotton seedling has been completely decom- 

 posed by the fungus in a somewhat dry site, the hyphse 

 which grow away from it form branching brown rhizo- 

 morphs, seeking fresh sources of food. The fungus is 

 ubiquitous in Egypt, and its sterile mycelium must be 

 regarded as a gigantic network, stretching through the 

 soils of all the country. 



It is strictly aerobic, grows freely on most culture 

 media, though with difficulty when the nitrogen is 

 presented as urea, and forms resting cells very quickly on 

 asparagin media, while it can infect cotton seedlings 

 under perfectly sterile conditions. The cotton plant is 

 immune when cork layers have been formed, though even 

 then it can be infected at wounds, but without any 

 notable injury. 



The chief interest of the disease lies in its absolute 

 dependence on temperature, and the consequent mis- 

 apprehension existing as to the effect of cold on cotton 

 seed. If germinating seeds, or seedlings, are kept damp 

 at a temperature of 20 C. with a fragment of " sore-shin " 



