72 
Margaret W. Rea 
carbon dioxide; the water-loss at the same time being reduced by 
reduction in the number of hydathodes, and by the more nearly 
erect position of the leaf. 
3 - The arrangement of the stomata varied according to the leaf 
surface, there being sometimes a marginal row on the under surface 
which was wanting on the upper side; but this character is variable. 
4. The stomata on the under surfaces varied markedly in size 
for the lower leaves of the normal and shade shoots, being large, 
medium or small; while on the upper surfaces in these shoots and on 
both sides of the leaves of the sun plant the medium size occurred. 
Hydathodes. 
1. Hydathode groups were present on the upper surfaces of all 
the leaves examined. 
2. They were most numerous towards the bases of the shoots, 
and only an apical group was present on the upper linear leaves. 
3. From the data obtained it is concluded that hydathodes are 
developed to a degree which is dependent upon the development 
of the vascular system of the individual leaves, upon the position 
of the leaves on the shoot, and also upon the habitat of the plant. 
Acknowledgments are due to Professor R. H. Yapp, at whose 
suggestion the work was commenced, for material; to Mr B. M. 
Griffiths for advice; also to Professor J. Small for material and his 
assistance in the preparation of the paper for publication. 
REFERENCES. 
(1) Darwin, F. On the relation between Transpiration and Stomatal Aperture. 
Phil. Trans. Roy. Soc., London, B, 207 , pp. 436-437. 1916. 
(2) Delf, E. M. Transpiration and Behaviour of Stomata in Halophytes. Ann. 
Bot., 25 , pp. 500-501. 1911. 
(3) Haberlandt, G. Physiological Plant Anatomy. Engl, transl. 1914. 
(4) Tenopyr, L. A. On the size and shape of cells in leaves of different forms 
on the same plant ( Campanula rotundifolia and Lobelia Erinus). Bull. 
Toney Bot. Club, Feb. 1918; ex Science Progress, No. 50, Oct. 1918, p. 216. 
(5) Tschirch, A. Ueber einige Beziehungen des anatomischen Baus der Assimi- 
lationsorgane zu Klima und Standort, mit specieller Berticksichtigung de$ 
Spaltoffnungs-apparates. Linnaea, N.F. 9 , p. 173. 1880-1882. 
(6) Weiss, A. Untersuchungen fiber die Zahlen- und Grossenverhaltnisse der 
Spaltoffnungen. Jahrb. f. wiss. Bot., 4 , pp. 166-167. 1865. 
(7) Yapp, R. H. Spiraea Ulmaria L., and its bearing on the problem of xero- 
morphy in marsh plants. Ann. Bot., 26 , pp. 826-828. 1912. 
