VEGETATIVE ORGANS 



II 





The ligule is a structure peculiar to grasses and it varies very 

 much. In some grasses it is a distinct membrane narrow or broad, 



with an even, truncate 

 or erose margin, or 

 finely ciliate. Very 

 often it is only a line or 

 fringe of hairs, whilst 

 in some it may be en- 

 tirely absent as in the 

 leaves of Panicum colo- 

 num. When it is a 

 membrane it may be 

 broad and oblong, 

 ovate and obtuse, or 

 lanceolate and acute. 

 (See fig. 13.) The func- 

 tion of the ligule is 

 probably to facilitate 

 the shedding of water 

 which may run down 

 the leaf, and thus 

 lessen the danger of 

 rotting of the stem 

 which is sure to follow, 

 if the water were to find its way into the interior of the sheath. 

 Sometimes, in addition to the ligule, other appendages may be 

 present in grass leaves as in Oryza sativa. Such outgrowths are 

 called auricles or auricular outgrowths. (See fig. 13.) 



The leaf-blade is well developed in the foliage leaves and in 

 most cases it follows directly on the sheath. But in bamboos and 

 some species of Ischsemum there occurs a short petiole or stalk 

 between the leaf-blade and the sheath. The sheath corresponds 

 morphologically to the leaf base of a leaf of other flowering plants. 



In grasses the leaf-blades usually grow more in length than in 

 any other direction and there is no limit to the length they may 

 attain. Some 



grasses have 



very short leaves, 

 long 

 leaf- 

 most 

 more 

 some 

 form, 

 linear, 



FlG. 14. — Shapes of leaf-blades. 



1, 7 and 8. Lanceolate ; 3 and 6. lanceolate - 

 2 and 5. linear ; and 4. ovate. 



others very 



ones. The 



blade in 



grasses is 



or less of 



elongated 



such as 



linear-lanceolate, 



lanceolate, etc. 



(See fig. I4-) ir i (; - *5- 



In a few grasses 1 and 



the leaf-blade is 



ovate, but this is a rare condition. Therefore, in noting the general 



shape of the leaf-blade the relation of the length to the breadth, 



the amount of tapering towards the apex and base and the nature 



of the apex should be considered. 



Margins of leaves. 

 Finely serrate ; 3. glandular ; 4 and 5. very minutely 

 seriate : 6. very minutely serrate and ciliate. 



