SELECTION WITHIN PURE LINES OF PESTALOZZIA 167 



in all selection studies since it is not improbable that in some cases small 

 mutations have arisen in the course of selection experiments, which have 

 not been detected and have produced effects attributed to selection. In 

 this experiment in the minus line of generation 14, culture 5, a distinct 

 mutation appeared which had a greater length of spore appendages 

 than any other culture encountered in the whole experiment. The spores 

 themselves were also longer, much more slender, and lighter in color than 

 those of any other culture seen during the whole range of my experience 

 with Pestalozzia. This form has since remained distinct through several 

 generations and will be studied further at a later date. It is mentioned 

 here merely to show the possibility that such mutations may account for 

 some of the results which are apparently due to selection. In the present 

 instance the mutation occurred in a plus direction but in the minus line 

 and so could hardly have escaped attention, but had it occurred in the 

 plus line, had it been somewhat less striking, and had it occurred in a less 

 carefully controlled experiment it might have escaped detection, and have 

 greatly confused the results of that experiment. 



That the new form was not a contamination from outside instead of a 

 mutation, was made practically certain because no such form had ever 

 been isolated from the surrounding country; because all culture work 

 was carefully done and the usual contaminating organisms were rarely 

 found in the cultures; because Pestalozzia is not a fungus which is likely 

 to be found as an air-borne contamination in cultures; and finally, because 

 blank plates were poured in many generations without ever securing any 

 growth of any organism. 



Experiment 2, carried on for more than one year, through twenty-five 

 generations, involving nearly 500 different cultures, and 50,000 spore 

 measurements, should have been a sufficiently thorough and long-con- 

 tinued study to demonstrate any effect of selection which might have ap- 

 peared. Since no such effect has been demonstrated we can only conclude 

 that the result of this experiment agrees entirely with that of experiment 1 

 and that it is not possible to produce lines distinct for lengths of spore 

 appendages by even long-continued selection. 



Selection of spores according to visible characters 



The selection of spores according to their appearance was now under- 

 taken as a check on the results of the previous selections. On account of 

 the small size of the spores of Pestalozzia considerable difficulty was ex- 

 perienced in finding a method by which the measured spores could be 



GENETICS 7: Mr 1922 



