618 BRITTON : VEGETATION OF THE 
Strands of sclerenchyma in the cortex are commonly found in 
these plants and are thought to be of value in strengthening and 
preserving the shape of the plant in excessive drought and wilting 
of the tissues. In size and number of vessels the root structure 
of Trichostema dichotémum is similar to that of the annual legumes, 
but the sclerenchymatous strands are wanting. Polygonum Con- 
volvulus, Ambrosia artemisiacfolia and Sarothra gentianoides have 
even larger vessels than the plants just mentioned, and seem to 
have nearly reached the limit of power to supply water to the 
upper portion of the plant. 
In the small lateral roots of perennial composite plants we find 
much cortical tissue of colorless cells that can doubtless store 
water to be used later by the plants. Moreover, the plants of 
this family whose roots were studied inhabit dry regions. This is 
true of Chrysanthemum Leucanthemum, Chrysopsis falcata, lonacts 
linarufolius, Artemisia caudata (biennial), Solidago nemoralis, An- 
tennaria neglecta, Gnaphalium obtusifolium (G. polycephalum) and 
Leptilon Canadense. 
In Salomonia biftora and Vagnera racemosa the endodermis of 
the small roots is interrupted or has some of its cells replaced by 
thin-walled cells opposite the points of the xylem as they appear 
in cross-section. This arrangement seems to provide for the 
transfer of water between the xylem and the cortex. 
ACKNOWLEDGMENTS 
The author here expresses his gratitude to Mr. Luman Andrews, 
of Southington, for kindly determining the species of Panicum 
and Sporobolus vaginacflorus ; to Mr. M. L. Fernald, of the Gray 
Herbarium, for identifying Carex Pennsylvanica; to Mr. L. M. 
Tarr, local forecast official of the New Haven office of the U. 3: 
Weather Bureau, for furnishing the records of temperature and 
precipitation ; especially is he indebted to Professor A. W. Evans 
for many kind suggestions in planning and carrying out these 
studies, for verifying the author’s determinations of plants, for help 
in determining several species, and for examining the microscopic 
Preparations and the manuscript. 
YALE UNIVERsITY. 
