1899.] NATURAL SCIENCES OF PHILADELPHIA. 221 



3.00 min. — Leaves assume a nearly horizontal position and the 



blade unfurled. 

 4.00 min. — Movement of one of the petioles still evident. 

 5.00 min. — Leaves assume the normal position. 



The main leader showed much quicker response than the laterals. 

 In removing this branch to the cold after it had assumed the 

 normal position in the heated room, it was found that the response 

 under the freezing temperature was not so rapid or marked as 

 when the shoot was moved from out of doors into a heated atmos- 

 phere. A slight response to the cold was evident in three minutes, 

 when the petiole began to curve slightly and the blade to roll. At 

 the end of five minutes, the larger leaves were well turned down 

 and rolled. At the end of ten minutes, the large leaves of one 

 of the shoots experimented upori had assumed the cold position. 



Fig. 1. — Branch in cold rigor position pliotograplied at one-miniite interval 



after being removed to a heated room. The hanging and inrolled 



position of leaves shown. 

 Fig. 2. — Branch photographed one minute after the first, showing that the 



movement of the leaves under the heat stimulus has beguu. 

 Fig. 3. — Branch with fully expanded leaves after a five-minute interval. 



All of the branches were stuck upright in pots filled with soil, 



and thus photographed. 



