DEVELOPMENT OF PLANTS 



391 



cells at the base of the node on the side of the stem next to the 

 ground, thus causing the stem to curve up (Fig. 282, C). You 

 can easily demonstrate this peculiar localization of growth by 

 cutting off a growing stem of grass and placing it horizontally 

 with one end embedded in moist sand and noting the curvature 

 of the node after a day. The leaves show wide variation in 

 structure and are doubtless one of the factors that have enabled 



Fig. 282. Habit of growth of one of the grasses: A, aerial stem termi- 

 nating in a branched inflorescence. B, underground stem or rhizome send- 

 ing up a new shoot from one of the nodes. C, section through the node of 

 a stem that has been placed horizontal, showing the sheathing leaf base, /, 

 and the beginning of the upward curvature of the stem. 



these plants to live under a variety of conditions. For example, 

 where the plants are exposed to drought or drying winds the 

 epidermal cells are very much thickened, stomata often sunken 

 in narrow furrows and practically all species have the power of 

 rolling up the leaves in dry seasons and thus reducing the leaf 

 surface and lessening transpiration. 



