BARBER: HEREDITY IN CERTAIN MICRO-ORGANISMS. 39 



and nine months the check was found to be still alive, but 

 the new race was no longer viable. 



In the summer of 1904 experiments were renewed in the 

 attempt to confirm earlier results, but, though experiments 

 were continued through several weeks, and many series of 

 vegetative rods isolated, all of them reverted to the spore- 

 forming type. These attempts were renewed in the autumn 

 of the same year, and again in the summer of 1905, but with 

 uniformly negative results. The original asporogenous cul- 

 ture of 1904 was continued through many subcultures, but 

 finally died. 



While no final conclusions can be founded on the results of 

 one successful experiment, there is good evidence from this 

 experiment that asporogenous races of bacteria, retaining 

 their characteristics for weeks at least, may be obtained by 

 selection of certain vegetative cells. But from the large pro- 

 portion of failures to obtain new races by the selection of 

 sporeless cells, it is evident that variations which result in 

 asporogenous types are rarely met with. 



GENERAL SUMMARY, 



In surveying the field in which these experiments lie, one 

 is at once impressed by the similarity between the new races 

 observed here and those arising in higher plants by mutation. 



We have in both the sudden appearance of a new type with 

 full-fledged characters arising independently of natural selec- 

 tion, and apparently independently of immediate environ- 

 ment. Successive generations of yeasts or bacteria doubtless 

 find their counterpart in successive cell generations in organs 

 of higher plants ; and new races arising among them are to 

 be compared with sports arising vegetatively in multicellular 

 organisms. 



While it appears that such variations are much more com- 

 mon among micro-organisms than in higher plants, it may 

 well be that this difference is only apparent, and that there 

 may be very many cell variations in higher plant organs 

 which undergo the same fate as that of hundreds of yeast 

 and bacteria cells which I isolated in my experiments, and 

 either fail to develop or revert to the normal type. There 



