C'liAP. IV. PASSIFLOEACE^. 153 



Paullinia. It was not in flower, yet bore long forked 

 tendrils. So that, Paullinia, with respect to its tendrils, 

 appears to bear the same relation to Cardiospermum 

 that Gissus does to Vitis. 



Passifloeace^. — ^After reading the discussion and 

 facts given by Mohl (p. 47) on the nature of the 

 tendrils in this family, no one can doubt that they are 

 modified flower-peduncles. The tendrils and the 

 flower-peduncles rise close side by side ; and my son, 

 William E. Darwin, made sketches for me of their 

 earliest state of development in the hybrid F.floribunda. 

 The two organs appear at first as a single papilla which 

 gradually divides ; so that the tendril appears to be a 

 modified branch of the 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 intemodes having the 

 power of revolving. It exceeds all the other climbing 

 plants which I have, examined, in the rapidity of its 

 movements, aid all tendril-bearers in the sensitiveness 

 of the tendrils. The internode which carries the upper 

 active tendril and which likewise carries one or two 

 younger immature intemodes, made three revolutions, 

 following the sun, at an average rate of 1 hr. 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 of all six revolutions was 



