Chap. IV. VITACE^J. 143 



seems to me as striking and curious an instance of 

 transition as can well be conceived. 



Cissus discolor. The young shoots show no more 

 movement than can be accounted tor by daily variations 

 in the action of the light. The tendrils, however, 

 revolve with much regularity, following the sun ; and, 

 in the plants observed by me, swept circles of about 

 5 inches in diameter. Five circles were completed 

 in the following times : 4 hrs. 45 m., 4 hrs. 50 m., 

 4 hrs. 45 m., 4 hrs. 30 m., and 5 hrs. The same tendril 

 continues to revolve during three or four days. The 

 tendrils are from 3 J to 5 inches in length. They are 

 formed of a long foot-stalk, bearing two short branches, 

 which in old plants again bifurcate. The two branches 

 are not of quite equal length ; and as with the vine, 

 the longer one has a scale at its base. The tendril 

 stands vertically upwards ; the extremity of the shoot 

 being bent abruptly downwards, and this position is 

 probably of service to the plant by allowing the tendril 

 to revolve freely and vertically. 



Both branches of the tendril, whilst young, are 

 highly sensitive. A touch with a pencil, so gentle as 

 only just to move a tendril borne at the end of 

 a long flexible shoot, sufficed to cause it to become 

 perceptibly curved in four or five minutes. It became 

 straight again in rather above one hour. A loop of 

 soft thread weighing one-seventh of a grain (9*25 mg.) 

 was thrice tried, and each time caused the tendril to 

 become curved in 30 or 40 m. Half this weight pro- 

 duced no effect. The long foot-stalk is much less 



