586 BRITTON: VEGETATION OF THE 
published a number of papers in the Botanical Gazette * and in 
the American’ Journal of Science,t but while the author points 
out the probable uses of certain structures they are not consid- 
ered from the ecologist’s standpoint. 
The present writer has examined the roots of a number of 
plants found growing upon the sand plains for the purpose of 
ascertaining to what extent the subterranean parts of the plants 
become especially adapted for taking up and holding moisture. 
Any corresponding adaptations of leaves and stems which have 
come to his notice are considered in the present paper. 
A microscopic study has therefore been made of the leaves of 
twenty-three species, the stems of three, the roots of thirty-five, 
and the rhizomes of seven. 
Histrotocy o¥ LEAVES AND STEMS 
The material examined was collected on the sand _ plains. 
Leaves of several species were preserved in formaldehyde solu- 
tion, but in some instances it was necessary to examine dried ma- 
terial which was first soaked in potash-water. All sections were 
cut by hand. 
PoLYTRICHUM PILIFERUM. — The central portion of the leaf is 
more than a single layer of cells in thickness, while the edges of 
the leaf are formed of a single layer and are rolled upward at the 
base. The thickened portion bears near the base of the leaf a large 
number of lamellae. The edges of the leaf roll in such a manner 
as to cover the lamellae, forming an excellent hindrance to the loss 
of moisture. The lamellae are doubtless capable of absorbing 
much water and are not greatly injured if they become dry. 
SYNTHERISMA SANGUINALIS. — About four layers of large watet- 
celis are found over the keel, forming more than half the thickness 
of the leaf (see /. 26, ¢). The entire epidermal layer is of similar 
colorless cells and forms about one third of the thickness of the leaf. 
wii 28 
can Gra- 
*Holm, T. A study of some anatomical characters of North Ameri 
mineae. Bot. Gaz, 16: 166-171, p/. 15. 219-225, pl. 21,22. 275-281, pl. 23) 74 
1891; 17: 358-362, d/. 27. 1892; 20: 362-365, p/. 26. 1895; 21: 357-30 P 
27, 28. 1896; 22: 403-406, pl. 20. 1896. 
t Holm, T. Studies in the Cyperaceae. Am. Jour. Sci. 1V. 3: 121-1 28, pl 4 
1897; 4: 13-26, f. 1-19. 298-305, f. 1-4. 18973 7: 171-183, f 4-9: 435-45™ 
J. 1-14. 1899; 9: 355-363, f. 7, 2. 1900; 10: 33-47, f t-a?. 266-284. TH! 
II: 205-223, f. 1-3. 190%; 14: §7-63, fi 1-7. 417-425, f- F-74- 190% 
