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A TEXTBOOK OF THEORETICAL BOTANY 



Fig. 925. — Heliatithus iuberosus. Tuber showing nodal ridges 

 and bud developing into an aerial shoot. 



Tubers on the main stems are formed, for example, in a climbing member 

 of the Asclepiadaceae {Ceropegia zvoodii), which is often grown in green- 

 houses (Fig. 926). The tubers are local thickenings of the nodes, including 



Fig. 926. — Ceropegia icoodii. Trailing shoot showing tubers 

 formed as swellings at the nodes. 



the bases of the pair of opposite leaves borne at the node, and their axillary 

 buds. They are generally not detached, but form adventitious roots in situ, 

 which attach them to the support (bark, etc.) on which the plant is climbing , 

 and so become new centres of growth, -it 



f 



