(Edema of the Tomato. 113 



The organic acids increase most rapidly at a temperature ranging 

 from 50 degrees to 57 degrees Fahr.* As the temperature rises above 

 this point they are gradually decomposed. Darkness or weak light 

 also favors their increase, and De Vriesf has shown that a periodicity 

 of increase or decrease of these acids exists corresponding to night and 

 day. In fact anything which interferes with oxidation serves to per- 

 mit their increase, while those conditions which promote oxidation 

 serve to decrease them.J According to Warburg it is not the direct 

 action of light which decomposes these organic acids, but the oxygen 

 set free during carbon assimilation. || 



Another effect of the feeble light and its short duration is the pro- 

 portionately small quantity of carbohydrates produced. Except in the 

 case of some shade plaots where direct solar light may be too intense 

 for normal assimilation, other things being equal the activity of 

 carbon assimilation increases neai'ly in proportion to intensity of solar 

 llght,l or as the plants exist under more favorable conditions of light. 



*De Vries, Ueber den Antheil der Pflanzensauren an die Turgorkraft wach 

 sender Organe. Bot. Zeit. 1883, S., 850. 



Warburg, Untersuchungen aus d. Bot. Inst. 2 . Tubingen, Vol. 2, Heft. I, 

 1886, p. 71. 



fDe Vries, Ueber die periodische Saurebildung der Fettplanzen, Vorlauifge 

 Mittheilung, Bot. Zeit., 1884. 



Ueber die Periodicitat im Sauregehalt der Fettpflanzen, Verslagen en 

 Mededeelingen der Koninkl. Akad. van Wetenschapen, Afd. Naturkunde, R. 

 P. Amsterdam, 1884. 



|Ward. On some relations between Host and Parasite. Proceedings Royal 

 Society, Vol. 47. 



II Warburg, Untersuchungen, etc,, pp. 77-92. 



•y Wolkoff . Einige Untersuchugen iiber die Wirkungen des Lichtes von 

 verschiedener Intensitat auf die Ausscheidung der Gase durch Wasserpflanzen. 

 Pringsheim's Jalirbiicher, Bd, 5, S. 1-30. 



Van Tieghem, Respiration des plantes submergees a la lumiere d. une bougii, 

 lieu de formation des gaz. Comptes Rendus, herbd. 1869, p. 482. 



Famintzin, Die Wirkung des Intensitat des Lichtes auf pie Kohlensaurerzer- 

 setzung durch Pflanzen, Bulletin de I'Acad. d. St. Petersburg, Vol. 26, 1880, 

 column 296-314. 



Pringsheim, Zur Kritik der bisherigen Grundlagen der Assimilationstheorie 

 der Pflanzen, Monatsberichte der Berliner Academie, vom Feb., 1881, S. 16 

 und 16, cited by Reinke, Bot. Zeitung, 1883, No. 42, 43 and 44. 



Ward, Proceedings Royal Society, Vol. 47. 



Sachs' Physiology. 



PfeflEer Pflanzenphysiologie. 



Detmer Lehrbuch der Pflanzenphysiologie. 



15 



