102 



BOTANY AND PHARMACOGNOSY. 



the work of assimilation, as in the case of certain green stems. 

 Then again there are cases in which the leaves are reduced, and 

 the work of assimilation is carried on exclusively bv the shoot- 



FiG. 67. Bryonia dioica. a, young, spirally coiled tendril; b, expanded and irritable 

 tendril; c, tendril which has grasped a support; d. tendril which has not grasped a sup- 

 port, and has undergone the old-age coiling. iVfcer Pfeffer. 



axes, as in most Cactacese, certain marsh-plants and others. On 

 the other hand the shoot-axis may be modified so as to increase the 

 assimilating surface, as by a flattening of the axis, as in some of 



