VEGETATIVE ORGANS 9 



instead of growing straight up through the sheath, pierce the leaf- 

 sheath, come out and then they grow out as branches. This may 

 be seen in the underground stolons of Panicum repots and in the 

 ordinary aerial branches of Arundo Don ax. Branches that pierce 

 through the sheaths are called extra-vaginal branches. (See fig. 10.) 



Fig. 10. — Extra-vaginal shoots of 

 I. Panicum repens and 2. Arundo Donas. 



Fig. n. — N'odes. 

 1. Glabrous node ; 2. bearded node 

 3. node cut longitudinally. 



The nodes are in most cases very conspicuous and they are 

 often found swollen. However, it must be remembered that the 

 enlargement at the node is not due to the increase in size of the 

 actual node, but due to growth in thickness of the base of the leaf- 

 sheath. (See fig. 11-3.) Nodes may be pale or coloured, glabrous, 

 hairy or bearded with long hairs. When the stem is erect the 

 nodes are short and of uniform size all round. But, if the stem is 

 bent down or tipped over by accident, the nodes begin to grow 

 longer on the lower side until a curvature sufficient to bring the 

 stem to the erect position is formed and then it ceases to grow. 



As already noted some perennial grasses have creeping stems 

 and stolons, while others may have rhizomes. The grass Cynodon 

 dactylon develops several underground stolons which are covered 

 with white scale leaves and whose terminal buds are hard and 

 sharp so that they may be able to make their way through the soil. 

 The rhizomes when continuous and elongated are usually sympodia 

 formed by the lower portions of the aerial shoots. The aerial 

 shoot comes into the air and its lower portion is continued by a 

 branch arising from a lower leaf axil beneath the soil. 



The leaf. — Leaves are two-ranked and alternate, and very 

 often they become crowded at the lower portions of the shoots so 

 as to form basal tufts, though they are farther apart in the upper 



