CH. V] LEAF-STEUCTURE 73 



II. The chlorophyll-tissue is between the vas- 

 cular BUNDLES, AND NOT CONFINED TO RINGS 

 SURROUNDING THEM. 



A. Conspicuous lacunse between the vascular bundles. 

 Stomata on both faces. Motor-cells occur. 



Lacunae large and rectangular. Motor-cells con- 

 fined to a flanking line on each side of the 

 mid-rib. 



Glyceria aquatica. Leaves folded and in section 

 V-shaped, hardly keeled, with sclerenchyma at apex. 

 Motor-cells each side of the mid-rib only. The large 

 square or rectangular lacunae bounded by stellate cells. 

 Papillae on epidermal cells. Vascular bundles midway 

 between upper and lower surfaces. 



Glyceria fluitans. Section V-shaped and keeled, the 

 roof of each polygonal lacuna arched, hence the " ribs " 

 on the upper surface are between the vascular bundles. 

 The latter lie nearer the lower epidermis. The epidermis 

 has papillse. 



Catabrosa aquatica and Hierochloe also come here, the former 

 with small lacunae, the latter with larger ones chiefly towards the 

 upper surface of the leaf. 



DigrapMs is also apt to have a few air cavities near the mid-rib. 



B. Lacunae none, or inconspicuous, the chlorophyll-tissue 

 filling up between the ribs. 



(a) Upper and lower leaf-surfaces parallel, or nearly 

 so, and much alike, the ridges being very low or 

 obsolete. Stomata equal or nearly so on both 

 surfaces. 



