I04 



BOTANY AND PHARMACOGNOSY. 



circumnutating movement of the stem, as in the morning glory, 

 Menispermum (Fig 65), etc. Climbers, however, ascend by 

 means of special structures, as the aerial roots of the ivy, and are 

 termed root climbers; or they may climb by means of leaves, as 

 in Clematis, and these are known as leaf climbers; still others 

 climb by means of tendrils, as in the grape and Bryonia and these 

 are known as tendril climbers (Fig. 66). These tendrils, which 

 are thread-like modifications of the stem, are in some cases pro- 

 vided with disk-like attachments for holding the plant in position, 

 as in the Virginia creeper. Twiners and climbers are sometimes 

 spoken of as lianes (lianas), particularly those of tropical 

 regions, where they form a prominent feature of the forest vege- 

 tation. The lianes usually have rope-like, woody stems, the 



Fig. 68. Rhizome of Podophyllum representing three years' growth: b^, the terminal 

 bud of last year; b^, the corresponding one of the present year; B.the terminal one of the 

 entire rhizome will develop in the spring of next year. U and L^ indicate the scars of aerial 

 "leaves of the two preceeding years' growth; b^ and Ifi, latent buds. — After Holm. 



formation of leaves being either suppressed or retarded, and they 

 often run for long distances over the ground and climb to the tops 

 of the tallest trees. They are also frequently characterized by an 

 anomalous stem-structure. 



Stems vary furthermore in size and form. While most stems 

 are more or less cylindrical or terete, other forms also occur, as 

 the flattened stems in the Cactacese ; triangular in the Cyperacese, 

 and quadrangidar in the Labiatse and Scrophulariacese. 



Hypogeous Shoots. — While most stems attain a more or 

 less erect position as in trees and shrubs there are others which 

 bend over to one side, or lie prostrate on the ground, and in some 



