86 . ELEMENTARY BOTANY. 



the under or outer side of the leaf, the latter bending upward ; 

 but on the opening of the bud the greater growth takes place 

 on the upper side. Floral leaves often exhibit such nutations, 

 as do also many stamens and styles. If the points of unequal 

 growth, instead of alternating from side to side, pass regularly 

 around the organ, a revolving nutation will be the conse- 

 quence. This is illustrated in twining plants and tendrils. 

 When they touch an upright object they continue their rota- 

 tion and thus twine around a support. Tendrils grow straight 

 until they have attained about three-fourths of their size. 

 They are then sensitive to contact, and are continually re- 

 volving; when they touch any object, a curvature takes place 

 and a number of revolutions are performed around the sup- 

 port. That portion between the point of contact and base 

 also coils in a corkscrew manner (in two directions, since 

 both ends are attached), thus bringing the plant nearer the 

 support. 



Plant in flower-pots some seeds of twining plants and of those that bear 

 tendrils, as Morning Glory, Pea, etc. Furnish a support around which they 

 may twine or to which the tendrils may cling. Watch these from day to 

 day, recording their development and behavior. Observe also some plants 

 of the native flora that exhibit these motions. 



