barber: heredity in certain micro-organisms. 9 



times ; in another, ten times. In both series the results were 

 negative so far as obtaining a permanently modified race is con- 

 cerned. It was evident in a number of cases that the first few 

 generations proceeding from a large cell consisted of abnor- 

 mally large cells, but after repeated budding the cell type re- 

 sumed its normal size. The character of the selected type was 

 noted in hanging drop cultures during the progress of the ex- 

 periments, and in tube cultures months after the completion 

 of the selection. 



In these experiments precautions were taken to avoid re- 

 selecting the same large cell in the subsequent selection. A 

 number of single large cells were deprived of their buds and 

 isolated in separate droplets, where they were observed to 

 continue to grow and to reach a size far exceeding the nor- 

 mal and to produce a new crop of buds. On being isolated 

 again, and a second time deprived of their buds, these cells 

 usually refused to form new offspring, and showed an irregu- 

 larity of outline indicating loss of turgidity and death. 



In the above series many cell generations intervened be- 

 tween selections, so that a new series was carried out with 

 another yeast to determine the actual number of generations 

 during which a variation in size persists — a difficult thing to 

 do in an ordinary hanging drop. These experiments were 

 conducted in two ways : First, by means of a very fine glass 

 rod or pipette, but little bent at the tip, a daughter cell was 

 separated from the mother at a time when the attachment 

 showed the relationship clearly. This daughter-cell was 

 isolated, and, when it had grown, its first bud was separated, 

 and so on. 



A series several generations long was successfully carried 

 out, but the conditions of the experiment were such that it 

 was difficult to get definite results regarding heredity. Either 

 observations had to be kept up night and day, or growth had 

 to be checked during the intervals in the experiment. This 

 last was accomplished by keeping the hanging drop at re- 

 frigerator temperature over night. However, this exposure 

 to lower temperatures, together with the possible injury to 

 cells in the process of separation, subjected them to abnormal 

 conditions; and no very satisfactory results were obtained. 



