Damping Off. 341 



freshly developed threads branch freely but not profusely ; they 

 are colorless, composed of elongated cells 9//-ll/y in diameter and 

 100//-200// in length. The protoplasm is finely granular and 

 contains numerous small rounded vacuoles. The branches extend 

 to an angle usually of between 30 and 60 degrees from the main 

 hypha and very near the point of attachment are a little curved 

 toward the point of growth of the same. At the point of attach- 

 ment with the parent hypha the branch is considerably smaller 

 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 situated 

 some distance from the latter, usually 15/^-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 diseased 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 can not, 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 8 cc. of water and 1 

 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 -1 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 transfers, if the growth 



