HISTOLOGY 



35 



and round, while those lying over the furrows between the vascular 

 bundles are large and are called motor or bulliform cells. The 

 presence of motor cells is a characteristic feature of the leaves of 

 many grasses. 



The continuity of both the upper and the lower epidermis is 

 interrupted by the stomata. Air-cavities are seen below these 

 stomata. The arrangement of the stomata, the shape of the guard 

 cells and the characteristics of the epidermal cells become clear on 

 examining a piece of epidermis. (See figs. 49 and 50.) 



The structure of the leaf of Panicum javanicum may be taken as 

 typical of the structure of the leaves of most grasses. The leaves 

 of Erwchloa polystachya, Cynodon and Paspalums are very much 

 like the leaves of Panicum javanicum in their internal structure. 



Considerable amount of variation, however, occurs in the leaves 

 of grasses especially as regards the arrangement of fibres and motor 

 cells. 



Fig. 51. — A portion of the transverse section of the leaf of Eriochloa polystachy. 



x 120 

 1. Motor cell ; 2. stomata; 3. sclerenchyma ; 4. chlorophyllous layer. 



Every large primary vascular bundle in the leaves of many 

 grasses possesses sclerenchymatous bands both above and below. 

 The other vascular bundles may have bands of sclerenchyma on 

 bot sides or on one side only or none. For example, in the leaves 

 of Panicum repcns both the primary and secondary bundles are 



Mo. 52.— Transverse section of a portion of the leaf of Panicum repens. x 120 

 I. Motor cells; 2. stomata; 3. sclerenchyma; 4. chlorophyllous layer. 



provided with sclerenchyma on both the sides, while those of the 

 third order may have it on one side or not. The hyaline margin 

 of this leaf and of the leaves of other grasses consists entirely of 

 sclerenchyma. (See fig. 53«) 



