V. EPINASTY AND HYPONASTY. 267 



A large number of ordinary leaves and leaflets and 

 a few flower-peduncles are provided with pulvini ; but 

 this is not the case with a single tendril at present 

 known. The cause of this difference probably lies in 

 the fact, that the chief service of a pulvinus is to 

 prolong the movement of the part thus provided after 

 growth has ceased ; and as tendrils or other climbing- 

 organs are of use only whilst the .plant is increasing 

 in height or growing, a pulvinus which served to 

 prolong their movements would be useless. 



It was shown in the last chapter that the stolons or 

 runners of certain plants circumnutate largely, and 

 that this movement apparently aids them in finding a 

 passage between the crowded stems of adjoining plants. 

 If it could be proved that their movements had been 

 modified and increased for this special purpose, they 

 ought to have been included in the present chapter ; 

 but as the amplitude of their revolutions is not so 

 conspicuously different from that of ordinary plants, 

 as in the case of climbers, we have no evidence on 

 this head. We encounter the same doubt in the case 

 of some plants which bury their pods in the ground. 

 This burying process is certainly favoured by the 

 circumnutation of the flower-peduncle ; but we do not 

 know whether it has been increased for this special 

 purpose. 



EPINASTY HYPONASTY. 



The term epinasty is used by De Vries * to express 

 greater longitudinal growth along the upper than 



* 'Arbciten des Bot. Inst., two terms as first used by Schim- 



in Wiirzburg,' Heftii. 1872, p. 223. per, and they have been adopted 



DC- Yries hae slightly modified in this sense by Sachs, 

 (p. 252; the meaning of the above 



