158 



CARL DOWNEY LA RUE 



Experiment 1. Selection for length of spores 



In this experiment the character studied was the length of the spore 

 from the tip of the proximal cell to that of the distal cell. In figure 1, 

 frequency polygons for this character are presented for six strains, of which 

 No. 29 was the one used in this experiment. Strain No. 29 was secured 

 from an isolation of fungi from the wood of a sapling of the Para rubber 

 tree, Hevea brasiliensis. Previous to its use in this experiment it had 

 been observed for eight consecutive generations in pure culture on Hevea 

 agar. The data concerning these generations are shown in table 3. 



The experiment lasted from January 1919 to June 1919 and included 

 ten selections, all of which were made exactly according to the method 

 described above. Through some unfavorable circumstance, one of the 

 selections for the eleventh generation failed to grow and the experiment 

 was thus brought to an end. The entire experiment was done in Sumatra, 

 and Hevea agar was used for growing all the cultures. 



TABLES 



Mean spore lengths of cultures of strain 29, grown prior to the initiation of experiment 1. Mea- 

 surements in //. 



Figure 4 shows the greatest mean spore length in each generation for the 

 plus selections and the least mean spore length in each generation for the 

 minus selection; the so-called intermediate line carried on without selection 

 is shown also. The figure thus shows the range of difference between the 

 plus and minus selections. In case an effect of selection were present, 

 this range should become greater. In this experiment, this is obviously 

 not the case, since the range does not become greater. It is true that it 

 increases at different times for a number of generations, but this increase 

 is followed by a corresponding decrease, so that in the end no permanent 



