616 BRITTON: VEGETATION OF THE 
we find the most interesting and most striking examples of special 
adaptations to xerophytic conditions. These adaptations result 
chiefly in the development of special water-holding cells or tissues 
in certain parts of the leaf or stem. In Spartina large colorless 
water-cells, called bulliform cells, are found at the bottom of the 
grooves of the upper surface of the leaf. The stomata are situ- 
ated along the slopes of the groove and when the bulliform cells 
give up their water the grooves close up, thus preventing in a 
large measure the further escape of water through the stomata. 
Strands of stereome and a thickened and rugose cuticle are com- 
mon in the graminaceous xerophytes. 
Spartina cynosuroides though an inhabitant of meadows and 
marshes is capable of growing on the sand plains, as it is found at 
Montowese. The microscopic anatomy of the leaf shows this 
grass to have a typical xerophytic structure as pointed out by 
O’Brien.* The roots have developed large lacunes (//. 27, is 
which primarily were probably for purposes of aération. It is 
doubtful if these lacunes can be of any use to the plant under 
xerophytic conditions. 
Andropogon scoparius exhibits a well-marked xerophytic struc- 
ture, as special water-cells occur on the upper surface of the leaf 
(fl. 26, g). The same may be said of A. furcatus, which has a 
similar though less fully developed xerophytic structure of the 
leaf. The root structure of this plant compensates for what the 
leaf tissues may lack in reservoirs for the storage of water. A 
portion of the root is perennial and the thickened nodes are stored 
with starch for the nutriment of the plant the following season. 
The appearance of these thickened rhizomes and the cell structure 
of the small roots are shown on #j/. 27. 
Cenchrus tribuloides also shows a well-developed xerophytic 
structure in the leaf. Sporobolus vaginaeflorus likewise is well 
fitted by the structure of both leaf and root to inhabit desert 
places. Many water-holding cells appear in the leaf and the root 
is provided with a very thick-walled endodermis, especially in the 
small root. Large roots show a modification of the structure 7 
favor of thinner walls. 
The sedges examined have the inside wall of the endodermal 
2 one 
* O’Brien, Mss. (see fifth footnote on p. 585). 
