(5) 



The main problem, undoubtedly, is the one which has already 

 been discussed. Are "pure lines" really pure ? uo heritable 

 variations occur v/it?iin the clone ? It is this problem 

 which is attacked in the present paper. 



A second problem, intimately connected with the first, 

 is presented by the very existence of diverse strains. How 

 did these diverse strains originate ? Or, to bring the 

 problem within the horizon of the experimentalist, can new 

 strains arise from old ones, and if so, how ? The number of 

 diverse strains which exist in nature is almost beyond belief. 

 In my own work withi Centropyxis, out of over thirty indivi- 

 duals, isolated from a single pipette-ful of debris, taken 

 from a single dead lotus stem, there were no tv'o which., after 

 a month's multiplication and careful study, could be surely 

 assigned to the same clone. .'.'here did these diverse races 

 come from ? How long have thiey been in existence ? How do 

 new races arise from existing races ? To these questions we 

 have, as yet, no answer. 



Plan of the present investigation. The object of my 

 work with Centropyxis was to find out whether heritable vari- 

 ations do or do not occur within a single clone. Since many 

 investigators have reported that such variations are not to 

 be found, it miay be taken for granted that it will be no 

 easy task to find them, even if they do occur. It is not suf- 

 ficient, then, simply to pick a character at random, and de- 

 termine whether its variations are or are not hereditary. 

 One must first show that diverse clones exist in the given 

 species, and tliat these clones differ from each other in cer- 

 tain inherited characters. Then these characters may be 



