J. MCA. KATER AND R. D. BURROUGHS. 



oxygen deficiency. Thriving cultures of Polytomella were sealed 

 in glass tubes, very little air space being left between the top of 

 the medium and the sealed end. Since no photosynthetic 

 organisms were present, it would seem as though the dissolved 

 oxygen of the medium should have decreased. At the end of 

 one week the cultures had died out and very few cysts had 

 been formed. 



MORPHOLOGICAL CHANGES ACCOMPANYING THE EXPERIMENTS. 



When a hay infusion culture is seeded with Polytomella citri 

 taken from a stock culture (one containing uncooked hay in dis- 

 tilled water) the organisms will multiply rapidly for a few days, 

 during which time staining with iodine will indicate the presence 



d 



FIG. i. Diagrammatic figures traced from photomicrographs of Polytomellas 

 stained with iodine. Solid black indicates starch. Equal magnification. (See 

 text for further explanation.) 



of relatively little starch (Fig. ia). At the end of from two to 

 five days it will be noticed that the starch increases to such an 

 extent that the entire cell seems filled with it (Fig. 16). It is at 

 this time that encystment occurs. Polytomella never encysts 

 except when the cell-body is filled with starch, and, on the other 

 hand, such a culture has never been found to be unaccompanied 

 by cysts. 



As stated above, all cultures used in this work were derived 

 from a single stock, and later cultures were seeded with active 

 ones taken from previous experiments. 



