X.] 



BOTANY. 



43 



72. The epidermis is studded with breathing pores, 

 stomates (Fig. 21), which usually consist of two 

 sausage-shaped superficial cells inclosing an oval 

 orifice. The stomates of most plants open more 

 widely in the light than in the dark, and this must 

 have the effect of promoting evaporation (Par. 27). 



nwn 



FIG. 21. Fragment of Epidermis with a Stomate. 



The glass-like sheen of the surface of leaves is due 

 to the texture and transparency of the epidermis under 

 which the cells full of green chlorophyll granules are 

 seen (Par. 16). 



73. The venation, or arrangement of the vascular 

 bundles in the leaf, is for the most part very different 

 in Dicotyledons and Monocotyledons. In the former, 

 one or more vascular bundles enters the petiole (or the 

 leaf itself if sessile), and usually either runs to the end 

 of the blade as a mid-rib, or sends a branch into each 

 division of the leaf ; while from each side of this mid- 

 rib branches are given off that branch again, and by 

 uniting form a network. In most Monocotyledons 

 either many vascular bundles enter the leaf and run 



