STUDIES OF IRRITABILITY OF PLANTS PEIRCE 



75 



position of such adjustment. A geranium, for example, growing on a window 

 sill, turns toward the light. If, after it has accomplished a. bend toward 

 the window, it be turned around, it will reverse the bend or make a new one, 

 again carrying the tip over toward the light. And this process may be 

 repeated indefinitely, with the same result so long as the plant can grow. 

 Such a plant is likely to become longer in the same length of time than one 

 beside it which has not been changed in position. If this is the eifect on 

 stems, the position of which is reversed only at long intervals — say every 

 other day or two — would this also be the case if the intervals were short? 

 The result of an experiment on mustard will throw some light on this question. 

 Seeds of Sinapis alba were sowed on II, 22, 1912, on greenhouse soil in 

 2-inch flower pots, six of which were put on turn-tables making four revolu- 

 tions a minute, seven on turn-tables making two revolutions each minute, and 

 seven on the shelf, and therefore getting light mainly from one side. These 

 were allowed to grow until the first leaves in the plumule began to show 

 and were thereupon measured, that is, on III, 12, 1912, nineteen days after 

 sowing. The length taken for measurement was that from the surface of 

 the soil to the tip of the plant. The data follow : 



Average lengfth of 29 seedlings in Pot I on M-minute turn-table. 4 . 08 cm. 



3.88 

 4.13 

 4.53 

 4.96 

 4.38 



101 " 4.32 " 



Average length of 24 seedlings in Pot I on J^-minute turn-table. 



101 



3.90 cm. 



4.25 



3.92 



3.20 



4.78 



4.01 



4.09 



4.02 " 



4.27 cm. 

 4.80 

 3.80 

 3.99 

 4.89 

 4.33 

 3.91 



4.28 " 



