DAMPING OFF. 267 



than either the diameter of the parent hypha or the main part of 

 the branch, and the septum separating the protoplasm of the 

 greater part of the branch from that of the parent hypha is situ- 

 ated some distance from the latter, usually 15/1-20,* from the 

 main thread. This portion of the branch then, the contents of 

 which are continuous with those of the parent thread, is clavate in 

 form. Species of Botrytis will occasionally be developed in dis- 

 eased tissue of this kind, and sometimes develop phenomena of 

 damping off similar to that produced by this fungus, though much 

 more rarely, and the mycelium in its early stages cannot so far as 

 I am able to tell be differentiated from this sterile fungus. But 

 if a culture of the mycelium be made, in the course of a few days 

 or in a week, if the mycelium be that of Botrytis the conidial 

 stage or the clasping organs will be developed. But if it be that 

 of this sterile fungus no such conidial stage will be developed. 



Pure cultures of the fungus have been obtained at two different 

 times. In the summer of 1892, from young cotton plants and 

 again in February, 1895, from young lettuce plants which were 

 damping off. It can quite easily be obtained in pure culture by 

 transferring some of the mycelium grown in the air of a moist 

 chamber, to some acidulated culture media. A very good medium 

 is made by placing cuttings of bean stems, 7 to 8 centimeters long, 

 in a culture tube and adding to this about 8cc. of water and one 

 drop of concentrated lactic acid. Several of these culture tubes 

 should be prepared, and .then sterilized in steam for two hours 

 per day for three or four days in succession. The bean stems 

 should project 2 to 4 centimeters above the liquid, and to the ends 

 of these the mycelium can be transferred with a flamed platinum 

 needle. Several transfers should be made and from portions of 

 the mycelium which have been previously examined to be certain 

 that mucors or other fungi are not present. Out of several trans- 

 fers, if the growth in the moist chamber has been made with 

 caution, a few pure cultures are quite likely to result. 



Bacteria will be shut out by the acid in the medium, and if the 

 culture is free from other fungi in a few days the mycelium will 

 be visible as a silky white growth which spreads over the surface 

 of the bean stems growing downward over them and also outward 

 onto the surface of the glass tube. This growth continues to ad- 

 vance for several days with quite an even advance edge to the 



