Nortu Haven SAND PLAINS 617 
cells very strongly thickened. This would seem to prevent the 
escape of moisture from the central cylinder to the outer portion 
in dry times, as the only means of transferring the moisture is 
through the pits. The sedges also have interesting structures of 
leaf and stem. Stenophyllus capillaris exhibits large water-cells on 
the upper surface of the leaf, which is almost reduced to linear. 
The stem is star-shaped in cross-section with stereome strands on 
the points and water-cells and stomata in the grooves. Cyperus 
Jiliculmis (pl. 26, a) has very large bulliform cells over the midrib, 
and when these cells lose their water the leaf folds. It also has 
a corm or tuberous root which is closely packed with starch and 
is doubtless a storehouse for both food and water. A very 
different leaf structure is found in Carex Pennsylvanica and C. 
Muhlenbergti, both inhabitants of the sand plains. Instead of the 
epidermal cells being very large for holding water there are several 
strands of colorless thin-walled cells running through the interior 
structure of the leaves between the mestome bundles. Though 
these strands seem to be regarded as lacunes, and in fact are called 
lacunes by most writers, they are not true lacunes, as they are 
spanned by delicate and undulating cell-walls in most of the 
material examined. In some cases these were broken down, but 
this might readily have occurred in cutting the hand sections. 
The writer considers these strands as internal water-storage tissue. 
In his “Report on a Botanical Survey of the Dismal Swamp 
Region,” Kearney mentions the rosette form of Linaria Cana- 
densis.* Certain other biennials like Verbascum Thapsus, Onagra 
biennis and Artemisia caudata exhibit the rosette habit during the 
first year and is doubtless of some value in preventing a loss of 
water through transpiration. The habit of these four species was 
observed by the writer on the North Haven sand plains. 
. But it is the annual plants with shallow root-systems, and 
having a short period of growth, that must suffer most in a time 
of severe drought. Such plants have woody roots in which the 
Primary structure disappears early-and the vessels are large and 
Numerous. Annual legumes are of this class, and the roots of 
Cassia Chamaecrista, Crotalaria sagittalis and Strophostyles helvola 
Show a number of large vessels in the secondarily thickened roots. 
“Kearney, T. H. Contr. U. S. Nat. Herb. 5: 386. 1900. 
