HISTOLOGY 



41 



The epidermal cells of this leaf are large and uniformly round. 

 (See figs. 66 and 67.) 



Fig. 66. — Transverse section of a leaf of Panicum rlavidum. X 20 

 i. Vascular bundle ; 2. sclerenchyma ; 3. motor-cells. 



In the case of most grasses the motor-cells are found in groups 

 of three, four or five between the vascular bundles. The central 

 motor-cell is usually the largest and it is somewhat obovate in 

 shape in a transverse section of the leaf. In the leaves of Panicum 

 javanicum and Eriochloa polystachya there are three or four motor 

 cells in the group and the group consists of four, five or rarely six 

 motor cells in the leaves of Eragrostis W Hide novi ana. When there 



Fig. 67. — Transverse section of a portion of the leaf of Panicum navidurn. x 150 

 1. Motor-cells ; 2. stomata ,- 3. sclerenchyma : 4. chlorophyllous layer. 



are distinct furrows between ridges these cells lie in the furrows 

 and they are many in number. In the leaves of Panicum repens 

 there are five to seven motor-cells in the furrows and the single 

 row of cells stretched between the motor-cells and the lower 

 epidermis in the furrow consists of more or less clear cells with 

 sparsely scattered small chlorophyll grains. (See fig. 52.) The 

 motor-cells occupying the furrows in the leaves of Aristida setacea 

 are more in number than in Panicum repens and are of a different 

 shape. All the cells lying in the furrow between the motor-cells 

 and the sclerenchyma are clear cells free from chlorophyll grains. 

 Although the motor-cells differ in shape from the ordinary 

 epidermal cells in most grasses, there are, however, a few grasses 

 in which the motor-cells do not differ very much from the epider- 

 mal cells except in size. For example, in the leaves of Panicum 

 colonum the motor-cells are just like the ordinary epidermal cells in 

 shape but are larger. (See fig. 64.) 

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