CHAPTER IV. 



ANATOMY" AND HISTOLOGY. 



The principal anatomical features observed in the 

 leaves of grasses — apart from finer histological details 

 into which it is not my purpose to enter — concern the 

 characters of the epidermis and distribution of the 

 stomata and hairs, the arrangement of the chlorophyll- 

 tissue, that of the mechanical tissue (sclerenchyma) and 

 the vascular bundles to which the venation and ribbing 

 of the leaves are due, and the presence or absence of 

 those peculiar thin-walled cells (motor-cells) which bring 

 about the infolding or inrolling of the lamina (see p. 25) 

 as they lose water, and, finally, the presence or absence 

 of conspicuous lacunse or air-spaces so characteristic of 

 aquatic species. Several observers have occupied them- 

 selves with these matters, and the researches of Schwen- 

 dener, Duval Jouve, Pfitzer, P6e-Laby, and others have 

 rendered it possible to group most of our grasses ac- 

 cording to the microscopic characters of the leaves, 

 somewhat as I have done in Chapter V. 



