104 C. D. Sherbakoff 



securing cultures from them.^ The cultures thus obtained were in all 

 respects similar to the original stock cultures, thus confirming the relia- 

 bilitj'- of the poured-plate dilution, 



CULTURE MEDIA 



It is a well-known fact among mycologists that under different 

 environmental conditions many fmigi vary considerably in their 

 macro- and microscopic characters. One of the most important 

 factors in variabilitj' is the substratum. According to Thom (1910), 

 certain characters in Penicillia appear only when the fungi are grown 

 on a certain medimn. Other instances of a similar nature might be 

 cited. 



Because of this variability of many fungi with variation in the sub- 

 stratum, it seemed indispensable in this study of Fusaria to use a number of 

 different media in order to find the extent of the variability in the Fusaria 

 and to determine, if possible, which media could be most profitably 

 employed in this kind of work. 



The so-called " natural " media, as well as artificial media, were used.^ 

 Those employed most extensively were potato tuber and stem plugs, and 

 hard agars of potato, lima bean, and oat. For the study of color produc- 

 tion, from 8 to 10 per cent of sugar (glucose) was added to one of the 

 above agars, usually to potato agar. In all other cases the agars were 

 used without glucose or with a small amount of it (0.5 per cent). In a 

 few instances the agars were more or less acidified by the addition of small 

 quantities of lactic or citric acid (from 1 to 3 drops of 50-per-cent acid 



8 The method employed was as follows: A number of drops (from eight to ten) of sterilized potato 

 broth were placed on a sterile glass slide. Dilution transfers were made from drop to drop until such a 

 dilution was secured that on removing a small droplet on the flattened end of a platinum needle it was 

 found by microscopic examination that in many cases a single spore could be obtained. From such a 

 drop nine transfers were made to a sterile, but somewhat greasy, cover glass. By placing the cover glass 

 over a tubular glass cell or a van Tieghem cell, each indi^•idual droplet could be examined viith a high- 

 power objective. Droplets containing no spore or more than one spore were wiped off at once with a 

 pointed piece of blotting paper. In thus removing spore droplets, the spores also were invariably removed. 

 Sterile water was placed in the bottom of the cell and the cover glass was sealed to the cell with sterile 

 water. The cells were then placed in a moist chamber for about twelve hours, and by this time the spores 

 had usually germinated and could be observed with much greater ease. This observation was almost 

 indispensable in the case of those species that produce numerous minute microconidia, as any such could 

 be easily detected at this stage. Only two or three droplets bearing single unmistakably germinatmg 

 spores were allowed to remain on the covers. At the end of twenty-four hours more, the growth of myceHum 

 from the single spores was usually sufficient to be seen with the unaided eye and could be transferred 

 readily with a finely pointed needle to a suitable medium. 



3 The media used were: (1) Natural — potato, bean, and pea stems; rye straw; canes of red rasj)- 

 berry; grains of rye, wheat, oat, barley, corn, and rice; corn meal and oatmeal; whole potato tubers and 

 plugs of potato tuber. (2) Artificial — potato, lima-bean, oat, corn, and nutrient agars (hard and soft, 

 from 1 to 3 per cent agar, neutral and more or less acidified, without and with different amounts of glucose). 



