154 
JOHN GRAY AND GEORGE J. PEIRCE 
manufacture also regulates the opening and closing of those slits in the 
epidermis through which alone carbon dioxide can enter at a rate sufficiently 
rapid to supply this necessary raw material of food manufacture. This 
factor regulating both food manufacture and stomatal opening is light. 
Conclusions 
The study of the stomatal reactions of the cultivated and wild species 
of grains has led to the following conclusions: 
1. The stomata of barley, wheat, oats, and rye plants open with light 
and close with darkness. 
2. Increase or decrease in the amount of light, when it has reached a 
minimum intensity, will have a corresponding effect upon the width of the 
stomatal openings. 
3. The opening and closing being accomplished by the changes in shape 
of the guard cells of the stomata, a minimum amount of moisture in the 
soil is required by each species in order to produce and maintain the tur- 
gidity of the guard cells without which changes in their shape are impossible. 
4. The moisture, soil, and light requirements of the different species 
are essentially alike, though not identical. 
Leland Stanford Junior University, 
California 
BIBLIOGRAPHY 
1. Pfeffer, W. Pflanzenphysiologie. 2te Auflage, 1897. Eng. transl. by Ewart, A. J. 
Oxford, 1900. 
2. Darwin, F. On the relation between transpiration and stomatal aperture. Phil. 
Trans. London, ser. B 207: 413-437. 1916. 
3. Lloyd, F. E. The physiology of stomata. Carnegie Inst. Wash. Pub. 82. 1908. 
4. Mohl, H. von. Welche Ursachen bewirken die Erweiterung und Verengung der Spalt- 
offnungen? Bot. Zeit. 1856. 
5. Schwendener, S. Ueber Bau und Mechanik der Spaltoffnungen. Monatsb. Preuss 
Akad. Wiss. Berlin, 188 1. 
6. Peirce, G. J. The botanical aspects of Stanford University. PI. World, 12: 245-252. 
1909- 
7. Stahl, E. Einige Versuche iiber Transpiration und Assimilation. Bot. Zeit. 52: 117- 
146. 1894. 
8. Buscalioni, L., and Polacci, G. Alteriori ricerche sull'applicazione delle pellicole di 
collodio alio studio di alcuni processi fisiologici delle piante ed in particolar modo della 
traspirazione vegetale. Att. 1st. Bot. Univ. Pa via. n.s. 7: 1902. 
9. Livingston, B. E. The relation of desert plants to soil moisture and to evaporation. 
Carnegie Inst. Wash. Pub. 50. 1906. 
DESCRIPTION OF GRAPHS 
In all the graphs the curves are made of broken lines. The different sorts are to indicate 
the following records: 
Continuous lines connecting the small circles indicate the opening and closing of the 
stomata. 
Broken lines of equal length form the temperature curves. 
Broken lines of two unequal lengths form the humidity curves. 
