Problems of Plant Physiology 53 



carbon into combination with hydrogen, yet the little green leaf in the 

 sunshine does it quietly and without getting hot" (66, p. 239). 



One of the tasks of the future is to ascertain, therefore, if possible, 

 the various ways by means of which green plants make their food 

 substances and to follow out the chain of processes completely. Green 

 plants get their energy from the sunlight and build up their structure. 

 They have done this in past ages, and of this we have an expression 

 in coal deposits, which are of proved vegetable origin (94). A knowl- 

 edge of these various plant processes is all the more important since 

 our timber supply is virtually gone. When we burn wood we release 

 the energy of the sunlight which was stored up in the plant by the 

 process of photosynthesis. By this transformation of potential into 

 kinetic energy the activities of the green plant are reversed. And when 

 we burn coal, formed as above indicated by green plants, which collected 

 the sun's rays of many thousands of years ago and stored them, we 

 release this energy in the form of heat by the process of combustion. 

 And so with our forests, nearing exhaustion as a fuel resource and 

 the end of our available coal in sight we realize that some other source 

 of energy must ultimately be obtained. The recent coal strike furnished 

 sufficient evidence to convince the railroads and other industries that 

 coal was necessary to keep them in operation. Possibly a successful 

 study of the various chemical and other processes of the chloroplast will 

 later assist in throwing some light on this very important subject. 

 With these suggestions and indicated problems some of which are old, 

 many recent, and others in progress, some idea may be gained of the 

 numerous opportunities for study which the subject of plant physiology 

 offers, 



LITERATURE CITED. 



1. PfefFer, W. Pflanzenphysiologie. Bd. 1, 1897; Bd. II 1904. 



2. PfefFer, W. Druck. u. Arbeitsleistungen durch wachsende Pflanzen. 



1893, p. 328. 



3. Kraus, G. Abh. Naturf. Ges. Halle. 1880, 1884. 15, 1; 16, 1. 



4. Kraus, G. Wasservertheilung i. d. Pflanze. 1880, II. p. 68. 



5. Czapek, F. Jahr, f. wiss. Bot. 1906, Bd. 43, p. 362-467. 



6. Nobbe, Versuchsst. 1875, Bd. 18, p. 279. 



7. Strasburger, Noll, Schenck and Schimper. A Text Book of Botany. 



Eng. Trans. 1898. 



8. Sachs, J. Text Book of Botany, 2 Ed. 1882. 



9. Pfeffer, W. Physiology of Plants. Eng. Trans. 1897, Vol. I. 



10. Schwartz. F. Unters. a. d. Bot. Inst. z. Tiibingen 1883, Bd. I. p. 135. 



11. Haberlandt, G. Physiologische Pflanzenanatomie. Dritte auf, 1904. 



12. Snow, L. M. Bot. Gaz. 1904, Vol. 37, p. 143. 



13. Bardell, E. M. Univ. of Wash. Pub. in Bot. 1915, Vol. I, pp. 1-9. 



14. Sachs, .J. Vorlesungen iiber Pflanzenphysiologie. 1887. 



15. Jost, L. Vorlesungen iiber Pflanzenphysiologie. 1908. 



16. Hannig, E. Zur Physiologie pflanzlicher Embryonen. Bot. Zeit. 

 1904, Bd. 62, pp. 45-80. 



17. Dixon and Joly. Annals of Bot. 1896, Vol. 8, p. 630. 



