Botanical Section 



[PT I 



the shoot, the sheaths are cylindrical and without strongly marked 

 keels. In the Oat and Couch-grass notice that the sheaths are split, 

 and the leaves are rolled in the shoot. Soft Brome-grass (Bromus 

 mollis, L.) is an example of a grass with entire sheaths, and 

 Cock's-foot (Daclylis glomerata, L.) shows the folding of the leaves 

 in the young shoots very well indeed. 



Near the surface of the ground the sheaths of many grasses, 

 either while quite young, or as they age, become characteristically 

 coloured. The colour is constant for each species, and may 

 either be present all round the sheath, or confined to the veins only. 



Fig. 6 



Fig. 7 



Fig. 6. Transverse section of young shoot of Poa trivialis x 20, showing the 



oonduplicate (folded) arrangement of the leaf -blades Bl^, Bl 2 etc. Sh. the 



outer entire sheath (shaded). K. Keel of sheath. 

 Fig. 7. Transverse section of young shoot of Phleum pratense x 20, showing 



convolute (rolled) arrangement of the leaf -blades BI X , Bl 2 etc. Sb. the 



split sheath. 



Leaf-blades. These are attached to the upper part of the 

 sheaths and may be either expanded or closed, i.e. the blade 

 may remain almost flat, or the two sides of its upper surface may 

 be folded one upon the other; or again the blade may be rolled 

 up like a roll of paper. This rolling or folding of the blade 

 may be only temporary and due to drought or exposure, but 

 in some species, e.g. Sheep's Fescue, this type of leaf is normal 

 and permanent. In order to understand more clearly this process 

 of rolling up and unrolling, etc., and to realise its great signifi- 

 cance, it is necessary to consider briefly the internal structure 

 of the blade and its modifications. See also Chap, n, p. 21. 



