46 GROWTH AND WORK OF PLANTS 



often the branching soon displaces the main trunk, and the various 

 stems may extend in various directions. The general position, 

 however, of the plant i$*erect. Where a number of individ- 

 uals start very close together, in age the outer ones may lean 

 more or less under the influence of light arid the need for room. 

 This is true with many shrubs which branch near the ground or 

 send up many stems from the underground portion. Erect 

 stems are self-supporting, the woody and supporting tissues 

 being sufficiently developed to give great strength and rigidity, 

 while the proportion in size and height is in harmony with the 

 supporting tissues. 



74. Climbing stems. Climbing stems are not self-support- 

 ing; they climb upon or around other objects. The pumpkin, the 

 morning glory, the grape, Japanese and English ivy, climbing 

 bitter sweet, climbing poison ivy, the rattan, etc., are examples. 

 The rattan grows in India, often attaining 

 several hundred feet in length. The more 

 slender species are used for wickerwork, 

 etc. Climbing stems secure themselves to 

 the object of support in various ways. 

 Root climbers develop numerous aerial roots 

 from the stem which take hold in the 

 crevices of the coarse bark of trees, as in 

 the climbing poison ivy, or they can lay 

 hold of smoother surfaces of trees or walls, 

 as the English ivy. Tendril climbers take 



ivy with disk-like hoM of ^ object of supp()rt by j^ 



slender outgrowths. In many cases these 

 tendrils are modified leaves or portions of leaves. In the pea 

 the terminal portion of the leaf and leaflets (the midribs) 

 forms the tendrils which coil around the object of support. 

 In the squash and some of its relatives, it appears that 

 the tendrils are the main veins of reduced leaves. In the 

 clematis, or virgin's bower, the petiole (paragraph 120) of the 

 leaf acts as the tendril and coils around the object. The dwarf 

 tropaeolum climbs in a similar way. In the Japanese (or Boston) 



