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CARL DOWNEY LA RUE 



of the minus selection. Another culture, which had a mean spore length 

 as nearly midway between the other two as could be found, was chosen as 

 the origin of an intermediate line to be carried on from generation to 

 generation without selection. 



From each of the chosen cultures plates were now poured. When the 

 spores had germinated, ten single spores were cut out from the plates 

 made from the plus-selection culture and the same number from the minus- 

 selection culture. From the intermediate culture only one single-spore 

 culture was made. See figure 3. 



FIGURE 3. Plan of method of selection used in experiments 1 and 2. A represents the 

 parent culture; B, the agar plate poured with a dilution of spores from A; C, the daughter cul- 

 tures grown from spores from B, of which L has the highest mean value for the selected character 

 and is chosen as parent of a plus-selected line; S has the lowest mean value for the selected char- 

 acter and is selected as parent of a minus-selected line; and I, with a mean as nearly intermediate 

 between those of L and S as possible, is used as parent of an unselected intermediate line; D, 

 the plates poured from cultures L, S, and I; and E, the daughter cultures grown from spores 

 isolated from the plates in D. L and S are again selected as parents of the plus and minus 

 lines, respectively, and I is carried on without selection. 



