oA BIOLOGY 

 oX^ y- LIBRARY 



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SELECTION WITHIN PURE LINES OF PESTALOZZIA 143 



to detect any effect of selection. This was among the first of the consider- 

 able series of investigations which appeared to bear out the JOHANNSEN 

 theory. 



The work of EWING (1914 a, 1914 b, 1916) is of particular interest be- 

 cause of the large number of generations during which he practiced selec- 

 tion. He studied an aphid, Aphis avenae, and found that selection, even 

 for eighty-seven generations, was totally without effect. 



The work of HANEL (1908) has received much attention and adverse 

 comment. HANEL concluded that selection was without effect on Hydra, 

 but it is doubtful whether the experimental results justified the conclusion. 

 More recently the status of HANEL'S work has been discussed and the ex- 

 periments have been repeated by L ASHLEY (1915, 1916). The latter 

 worker took account of the sources of error in HANEL'S experiments and 

 carried out so excellent an investigation as to leave no doubt that selec- 

 tion within the genus Hydra is ineffective. 



A number of other investigators have secured results which substantiate 

 the work of JOHANNSEN. Some of them have made careful investigations 

 which are of considerable value. In other cases the results of loosely 

 planned and brief experiments have been recorded. For one to- believe, 

 because selection for one generation within a line has had no effect, that 

 selection is therefore in all cases ineffective, requires a very sanguine tem- 

 perament. There was ground for the protests of PEARSON (1910) and 

 HARRIS (1911) that the pure-line theory had been too readily accepted 

 before adequate evidence had been presented. However, all in all, a 

 considerable body of data supporting JOHANNSEN has been secured, some 

 of it exceedingly hard to refute. Until recently the results of all investi- 

 gations seemed only to add more evidence in support of the theory. 



Within the last few years, however, more and more conflicting evidence 

 has been amassed, partly through critical analysis of the older data, and 

 partly by new experimentation. JOHANNSEN'S experiments have been 

 criticized because they were not carried on for a sufficiently large number 

 of generations. By statistical analysis PEARSON (1910) found that there 

 was some evidence that JOHANNSEN'S results really showed inheritance 

 of somatic variations within pure lines. ROOT (1918) has discounted 

 EWING'S results because the organism concerned is one which in nature 

 is highly stable, its lack of variability affording at the start little ground 

 for hope that new strains could be produced. 



Several objections have been offered to the conclusions of JENNINGS 

 from his work on Paramecium. One is that he studied size characters 

 which are highly variable under different environmental conditions. These 



GENETICS 7: Mr 1922 5 7 J 7 9 



