2-76 Journal of Agricultural Research voi. iv. No. 3 



soil and left for a week or more before they are again observed. In a 

 number of cases in such cultures the plasmodium passed through the skin 

 of the tuber and killed some of the cells beneath the epidermis, but no 

 typical sori have been produced. 



Although the infection experiments have not yet given satisfactory 

 results, the writer is strongly of the opinion that the plasmodium which 

 he has in culture belongs to 5. subierranea. These plasmodia have been 

 obtained more than 100 times from cultures of germinating spores. 

 All of the Plasmodia are alike in appearance, and many of them have 

 been seen to engulf the amoebae of 5. subierranea as they crawl about 

 over the agar. A considerable number of the plasmodia have been 

 isolated and grown separately on Lima-bean agar. By making trans- 

 fers about once a week they can be kept in an active growing condition. 

 Some of them have been obtained in pure culture, but such cultures soon 

 become abnormal and die. Some evidence has been gained that if either 

 certain bacteria or fungi be added to the culture, the plasmodium flour- 

 ishes. This is in agreement with obser\^ations made by Pinoy (15) on 

 other slime molds. 



Some of the plasmodia have been induced to crawl up on glass slides, 

 where they can be fixed by dipping the slides in Flemming's weaker 

 solution. When stained with the triple stain, numerous nuclei can be 

 seen. Near the center of each nucleus is a rather conspicuous red- 

 staining nucleolus. In size and staining reactions, as well as in their 

 general appearance, these nuclei resemble very closely those in the 

 Plasmodia within the living potato cells. 



If a culture is allowed to become dry, the plasmodium encysts, as is 

 common among the Myxomycetes. In some instances, when a plasmo- 

 dium is transferred to a fresh medium, the streaming motion stops. The 

 Plasmodium then breaks up, and certain portions of the mass crawl 

 slowly away and soon produce fruiting bodies that closely resemble 

 those of Polysphondylium. This mass as it crawls along builds a central 

 stalk composed of irregular-shaped cells, much as has been described for 

 members of the Dictyosteliaceae. The stalk may lie flat on the medium 

 for a distance of several millimeters, but sooner or later it bends upward 

 and serves as a sporophore. The stalk, which varies both in length and 

 in breadth, is sometimes composed of a single layer of cells, but often is 

 five or six cells in breadth. These sporophores frequently branch several 

 times. The spores are bom in much the same way as has been described 

 by Brefeld (i) for the genus Dictyostelium. They are regularly cyl- 

 indric and about twice as long as broad. On germinating they give rise 

 to amoebae, pseudoplasmodia, and, later, to fruiting bodies like those 

 just described. No other kind of fruiting bodies have been observed. 

 Although it was not to be expected that a fungus with a true plasmodial 

 stage would give rise to a pseudoplasmodium, this, nevertheless, seems 



