CH. iv] Key to Vegetative Characters 29 



doubt by cutting the shoot across transversely with a sharp 

 knife. The arrangement of the young leaves can then be easily seen 

 with a lens (see Figs. 6 and 7). If the leaves are rolled in the shoot 

 the latter has a cylindrical shape ; if the leaves are folded the shoot 

 is more or less flattened. If hairs are present, it should be noticed 

 whether they are most abundant on the sheath or blade. Also, 

 whether they are most abundant on the upper or lower surface of 

 the blade. Again the student should observe whether the hairs 

 are short and densely crowded together, giving a velvety surface ; 

 or whether they are long, or scattered, or confined to the ribs, 

 leaf-margins, etc. 



In all the species included in the key the sheaths are split, 

 except where the contrary is stated. It is frequently difficult 

 to decide whether the sheaths of some grasses are entire or 

 split especially when the plants are young. This character has 

 for this reason been given a secondary place in the key. In 

 describing the ligule of any species as long, short, acute, etc., 

 reference is always made to the ligule of the uppermost leaf. 

 This is necessary, because in some grasses the ligules of the upper 

 and lower leaves differ considerably from each other in the relation 

 of length to breadth, etc. 



It should be observed that the key is based wholly upon 

 the grasses while in their young and undeveloped condition, i.e. 

 before flowering. As the plants mature they frequently alter 

 somewhat as regards hairiness, smoothness, shoot section, etc. 

 For example the sheaths of the young shoots of Cock's-foot and 

 Rough-stalked Meadow-grass are quite smooth it is only the 

 sheaths of their flowering culms which are rough. Hence in 

 dealing with the plants in flower, reference must be made to 

 Chapters v and vn. 



It is very desirable that not only the leaves, but also the roots 

 and stolons or rhizomes if present should be examined, as 

 these often afford conspicuous distinguishing characters. Occa- 

 sional reference has been made in the key to the habitats of species, 

 but only as a confirmatory point. 



One or two exotic species have been included because of their 

 occasional introduction into British agriculture and this remark 

 applies also to the other keys. 



