222 THE LAW OF JOHANNSEN. 



(and similar work on uni-cellulars). What relation do these 

 experiments have to Johannsen's work with pure lines of 

 beans and peas and so, and especially, are the results compat- 

 ible with what we have called Johannsen's law, with the qual- 

 itative stability of genes? At first sight there seems to be no 

 relation, but evidently some of the authors think their results 

 to have a direct bearing upon the problems touched upon by 

 Johannsen. F. M. Root says in his paper: The main problem, 

 undoubtedly, is the one which has already been discussed. 

 Are "pure lines" really pure? Do heritable variations occur 

 within the clone? It is this problem which is attacked in the 

 present paper." And in his conclusions: "The further idea, 

 that within one of these "pure lines' no variation in genetic 

 constitution is possible, except by a sudden mutation, large 

 or small, is not direct observation but hypothesis". "But of late 

 the tide seems to be turning somewhat". 



We certainly admit that the idea, that no variation in ge- 

 netic constitution is possible within pure lines, is a hypothesis. 

 That is to say, the hypothetical part of the statement is the 

 assumption that this absence of variation, and ineffectiveness 

 of selection within such material is due to the fact, that every 

 individual is pure for its genotype, which is the same as that 

 of all the others. The absence of variation and ineffectiveness 

 of selection of real pure lines is fact, observation, and not hy- 

 pothesis. Before we discuss again the effectiveness of selection 

 in clones and pure lines it is well to repeat, that there is only 

 one instance recorded in literature, and this is the in- 

 stance of Castle's interpretation of Hoshino's work on the 

 flowering-time of the pea. We say Castle's interpretation, be- 

 cause Hoshino does not himself, find evidences for the effect- 

 iveness of selection in his results with pure lines. 



Now the only point on which we beg to differ with Root and 

 Jennings is, that we do not see that "the problem attacked in 

 the paper" is really that which Root states in the words: "Are 

 pure lines really pure" Some authors mix up the term "clone" 

 and "pure line." Root certainly does not, but the fact that he 



