TENDRIL-BEARERS. 83 



by the next genus, Cissus. This genus, as we shall immediately 

 see, produces well-developed tendrils and ordinary bunches of 

 flowers ; but there is no gradation between the two states. If 

 the genus Vitis were unknown, the boldest believer in the modi- 

 fication of species would never, I suppose, have surmised that 

 the same individual plant, at the same period of growth, would 

 have yielded every possible gradation between ordinary flower- 

 stalks for the support of the flowers and fruit, and tendrils used 

 exclusively for climbing. But the vine clearly gives us this case ; 

 and it seems to me as striking and curious an instance of tran- 

 sition as can well be conceived. 



Cissus discolor. — The young shoots show no more movement than 

 can be accounted for 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 w r ere completed in the following 

 times : — i h. 45 m., 4 h. 50 in., 4 h. 45 m., 4 h. 30 m., and 5 h. The 

 same tendril continues revolving during three or four days. The 

 tendrils are from 3| 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 is 

 bent abruptly downwards ; and this position is probably of service 

 in keeping it out of the way of the revolving tendril. 



The two branches whilst young are highly sensitive ; for-I found 

 a touch with a pencil so gentle as only just to move the tendril 

 which was borne at the end of a long flexible shoot, sufficed to 

 cause it to become perceptibly curved in four or five minutes ; the 

 tendril became straight again in rather above one hour. A loop 

 of soft thread weighing one-seventh of a grain was thrice tried, 

 and caused the tendrils to become curved in 30 or 40 m. : half 

 this weight produced no effect. The long foot-stalk is much 

 less sensitive, for slight rubbing produced no effect ; but pro- 

 longed contact with a stick caused it to bend. The two terminal 

 branches are sensitive on all sides ; if a number of tendrils be just 

 touched on different sides, two branches of the one on their inner 

 sides, two on their outer sides, or both branches on the same side, 

 in about a quarter of an hour they present a curiously different 

 appearance. If a branch be touched at the same time with equal 

 force on opposite sides, both sides are equally stimulated and 

 there is no movement. At the beginning of my work, and before 



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