TENDRIL-BEARERS. 89 



I have only seen, but was not enabled carefully to observe, one 

 other climbing Sapindaeeous plant, namely Paullinia. It was not in 

 flower, yet thus it bore fine long forked tendrils, differing from 

 Cardiospermum. So that, in its tendrils, Paullinia apparently bears 

 the same relation to Cardiospermum that Oissus docs to Vitis. 



Passifloraceje. — After reading the discussion and facts given 

 by Mohl (S. 47) on the nature of the tendrils in this family, no 

 one can doubt that they are modified flower-peduncles. The ten- 

 drils and true flower-peduncles rise close side by side ; and my 

 son, Mr. W. E. Darwin, made sketches for me of their earliest 

 state of development in the hybrid P.Jloribunda. The two organs 

 at first appear as a single papilla which gradually divides ; so that 

 I presume the tendril is a modified branch of a single flower- 

 peduncle. My son found one very young tendril surmounted by 

 traces of floral organs, exactly like those on the summit of the 

 true flower-peduncle at the same early age. 



Passiflora gracilis. — This well-named, elegant, annual species 

 differs from the other members of the group, observed by me, in 

 the young internodes having the power of revolving. It exceeds 

 all other climbing plants in the rapidity of its movements, and all 

 tendril-bearers in the sensitiveness of its tendrils. The internode 

 which carries the upper active tendril and which likewise carries 

 one or two young immature internodes, made three revolutions, 

 following the sun, at an average rate of lh. 4 m.; it then made, 

 the day becoming very hot, three other revolutions at an average 

 rate of between 57 and 58 m. ; so that the average rate of all six 

 revolutions was 1 h. 1 m. The apex of the tendril described 

 ellipses, sometimes narrow and long, sometimes broad and long, 

 with their longer axes inclined in slightly different directions. 

 The plant can ascend a thin upright stick by the aid of its ten- 

 drils ; but the stem is too stiff for it to twine spirally round a 

 stick, even when not interfered with by the tendrils, which had 

 been successively pinched off at an early age. 



When the stem was secured, the tendrils were seen to re- 

 volve in nearly the same manner and at the same rate as the 

 internodes. The tendrils are very thin, delicate, and straight, 

 with the exception of the tips, which are a little curved ; they are 

 from 7 to 9 inches in length. A half-grown tendril was not sen- 

 sitive ; but when nearly full-grown they are extremely sensitive. 

 A single delicate touch on the concave surface of the tip soon 

 caused it to curve, and in two minutes it formed an open helix. 

 A. loop of soft thread weighing ^nd of a grain (equal to only two 



