cH: v| LEAF-STRUCTURE 73 
II]. THE CHLOROPHYLL-TISSUE IS BETWEEN THE VAS- 
CULAR BUNDLES, AND NOT CONFINED TO RINGS 
SURROUNDING THEM. 
A. Conspicuous lacune between the vascular bundles. 
Stomata on both faces. Motor-cells occur. 
Lacune 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 lacune bounded by stellate cells. 
Papille 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 papille. 
Catabrosa aquatica and Hierochloe also come here, the former 
with small lacune, the latter with larger ones chiefly towards the 
upper surface of the leaf. 
Digraphis is also apt to have a few air cavities near the mid-rib. 
B. Lacune 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. 
