182 CARL DOWNEY LA RUE 



will be finally determined by numerous investigations with various or- 

 ganisms, involving infinite care and toil. There is need of more investiga- 

 tions of the type which JENNINGS has made on Paramecium and Difflugia, 

 but carried for longer periods, with organisms more favorable for study, 

 if they may be found. 



Nothing has been said in this paper, of the bearing of the "pure-line" 

 hypothesis on theories of evolution. Almost every worker who has made 

 careful biometric studies of highly variable groups has recorded the occur- 

 rence of mutations or "something like mutations." JENNINGS, ROOT, 

 MAST, and HEGNER have all recorded them for the lower animals. BAR- 

 BER (1907) noted the occurrence of mutation in yeasts; STEVENS (1920) 

 has reported a number of mutations in Helminthosporium ; and the writer 

 has found mutations in Pestalozzia. It is unnecessary to catalogue the 

 numerous cases of mutation recorded in various groups of higher plants 

 and animals. Further careful study will doubtless reveal many more. 

 When more is known of their occurrence, frequency, and reaction to 

 environment, to other existing organisms, and to one another, may we not 

 be able to conceive of evolution, even without cumulative growth of char- 

 acters by the selection of fluctuating variations? 



CONCLUSIONS 



Selections according to progeny within pure strains of Pestalozzia were 

 made for length of spores for ten generations, and for length of spore 

 appendages for twenty-five generations, without result. Selections ac- 

 cording to visible characters were made for spore length for ten genera- 

 tions in one experiment and for six generations in another, without 

 establishing differences between the plus-selected and minus-selected lines. 

 Whatever method and strain may be employed, selection is totally in- 

 effective in establishing distinct lines within pure strains of Pestalozzia 

 Guepini. 



Mutations which give rise to lines significantly different from the parent 

 lines, infrequently occur. 



LITERATURE CITED 



BARBER, M.A., 1907 On heredity in certain micro-organisms. Kansas Univ. Sci. Bull. 4, 48 pp. 

 EWING, H. E. 1914 a Pure line inheritance and parthenogenesis, Biol. Bull. 26: 25-35. 

 1914 b Notes on regression in a pure line of plant lice. Biol. Bull. 27: 164-168. 

 1916 Eighty-seven generations in a parthenogenetic pure line of Aphis avenae Fab. Biol. 



Bull. 31:53-112. 



HANEL, ELISE, 1908 Vererbung bei ungeschlectlicher Fortpflanzung von Hydra grisea. Jenaische 

 Zeitschr. 43:221-372. 



