142 SENSITIVENESS OF THE APEX Chap. IIL 



other trial, for it occurred to us that sensitiveness is 

 easily affected by external conditions, and that radicles 

 growing naturally in the earth in the early spring 

 would not be subjected to a temperature nearly so 

 high as 70° F. We therefore allowed the radicles 

 of 12 beans to grow at a temperature of between 

 55° and 60° F. The result was that in every one of 

 these cases (included in the above-described experi- 

 ments) the radicle was deflected in the course of a few 

 hours from the attached object. All the above re- 

 corded successful trials, and some others presently to 

 be given, were made in a sitting-room at the tempera- 

 tures just specified. It therefore appears that a tem- 

 perature of about, or rather above, 70° F. destroys 

 the sensitiveness of the radicles, either directly, or 

 indirectly through abnormally accelerated growth ; 

 and this curious fact probably explains why Sachs, 

 who expressly states that his beans were kept at a 

 high temperature, failed to detect the sensitiveness of 

 the apex of the radicle. 



But other causes interfere with this sensibility. 

 Eighteen radicles were tried with little squares of 

 sanded card, some affixed with shellac and some with 

 gum-water, during the few last days of 1878, and few 

 first days of the next year. They were kept in a room 

 at the proper temperature during the day, but were 

 probably too cold at night, as there was a hard frost at 

 the time. The radicles looked healthy but grew very 

 slowly. The result was that only 6 out of the 18 

 were deflected from the attached cards, and this only 

 to a slight degree and at a very slow rate. These 

 radicles therefore presented a striking contrast with 

 the 44 above described. On March 6th and 7th, when 

 the temperature of the room varied between 53° and 

 59° F., eleven germinating beans were tried in the 



