A peculiar Case of contact Irritability 



By F. Grace Smith 



In connection with some experiments upon factors determining 

 the radiation of shoots, several pots of bush-beans were grown in 

 the dark. When the seedlings, perfectly etiolated, were about 20 

 inches high and had developed their first leaves, a peculiar adjust- 



ment was noticed in them. Tile peti- 

 oles had arranged themselves in par- 

 allel planes. Another set of beans 

 was planted in 6-inch pots, one pot 

 kept in a black box, the control ex- 

 periment in a propagating room of the 

 greenhouse, which was lighted mostly 



from overhead but partly from the 

 north. Each pot contained ten beans 

 • in sphagnum moss, planted in a circle, 

 2 cm. apart with the hypoctyl of each 

 turned toward the center of the pot. 

 The box, in which the experiment was 

 carried on, was absolutely dark, ex- 

 cept when the plants were watered 

 and observed, a few minutes each day. 

 In three weeks this parallel adjust- 

 ment was seen in the pot kept in the 

 dark ( Fig. 1 ) . There was but one ex- 

 ception in the eight seeds which ger- 

 minated. No such adjustment could 

 be seen in seedlings grown in light, 

 or in succeeding experiments in the 



light. 



To determine if this position was constant, other pots were 

 planted in the same way, using eight seeds to a pot in most cases. 

 Not every pot showed so large a proportion of petioles, in parallel 

 planes but in almost every case more than three, usually four or five, 



( 190 ) 



Fig. 1. 



