Fusaria of Potatoes 105 



to 10 cubic centimeters of the medium) ; otherwise they were used as they 

 were after the process of cooking and sterilizing. 10 



The method of preparing all natural media was very simple. It con- 

 sisted in cutting suitable pieces, tubing, and sterilizing in an autoclave 

 for twenty minutes at fifteen pounds pressure. Enough distilled water 

 was added to the tubes to keep the cultures in good growing condition 

 for from three to four weeks, the exact amount, of course, depending on 

 the size and succulence of the material used. The decoctions that were 

 most commonly used were prepared in the following ways: 



Potato decoction. — Two hundred grams of peeled potato tubers were 

 sliced, 1000 cubic centimeters of distilled water was added, and the material 

 was cooked for about forty minutes in a double boiler. The clear liquid 

 was then decanted and the volume restored. 



Lima-bean and oat decoctions were prepared by soaking 100 grams of 

 ground lima beans or oats in 1000 cubic centimeters of distilled water at 

 60° C, in an incubator for an hour. The liquid was separated by strain- 

 ing through cheesecloth and the volume was restored to the original 1000 

 cubic centimeters. 



Corn meal decoction was prepared as described by Shear and Wood (1913) ; 

 that is, from about 35 to 40 grams of corn meal were treated in the same 

 way as 100 grams of lima beans or oats in the preceding case. 



For the artificial media, to 1000 cubic centimeters of a decoction were 

 added agar (10, 15, or 30 grams, these amounts corresponding respectively 

 to soft, medium, and hard agar) and glucose (0 to 100 grams), and the 

 whole was cooked in a double boiler over a free flame for an hour, or, 

 more exactly, until all the agar was well dissolved. The liquid was then 

 tubed, plugged, and sterilized in the same way as were the natural media. 



At the present stage of this work, it seems that all the labor spent on 

 using so many different media was more or less wasted. It seems that 

 the same results could as well be obtained with but a few good media, 

 preferably the following: a hard oat agar (without glucose), a stem and 

 tuber plug, and a potato agar with about 5 per cent of glucose. All other 

 media used in the course of this work did not prove to be of any specific 

 value, and at the best gave the same results that were obtained with 

 those just named. 



"> When an acid was added to an agar this was done after the medium was sterilized, the medium then 

 being quickly cooled. This quick cooling was necessary because otherwise an acidified agar often would not 

 solidify as well as it should. 



