164 PHOTOSYNTHESIS 



It does not seem pertinent to follow Pringsheim's further deductions. 

 Rut his experimental results indicate this fact. That a normal cell con- 

 taining chlorophyll in an apparently unchanged condition and exposed to 

 bright light and an atmosphere containing carbon dioxide is incapable 

 of photosynthesis in an atmosphere free of oxygen. It appears, there- 

 fore, that besides the conditions of light, chlorophyll, temperature, and 

 carbon dioxide supply, other conditions are essential and these are inti- 

 mately associated with the respiration of the protoplasm. The latter is 

 an important internal factor affecting photosynthesis, in addition to the 

 chlorophyll-content and the number of chloroplasts. The exact manner 

 in which these two processes of respiration and photosynthesis may be 

 linked is still an open problem. 



There have been observed some quantitative relations between photo- 

 synthetic activity and respiration. The leaves of the light-green or yellow 

 varieties of the plants investigated by Plester ^^^ showed a lower rate of 

 photosynthesis than the varieties rich in chlorophyll. Similarly the former 

 had a lower rate of respiration. Thus, while it is evident that there is 

 no parallelism between chlorophyll-content and rate of photosynthesis, 

 the quotient respiration — photosynthesis is more constant. This quotient 

 for the light-green varieties was found to be as follows: Ptelea= 1.77. 

 Catalpa—1.72, Mirabilis = 2.0, Ulmus = 2.0, Populus = 2.1, Atiplex 

 =. 1.3. The latter plant exhibits rather erratic photosynthetic rates. 



A correlation between respiration and photosynthetic rates was also 

 noticed by Henrici.^^* She found in a study of alpine and low land plants, 

 that those plants which had a high photosynthetic rate also had a high rate 

 of respiration and vice versa. Boysen-Jensen ^^^ found that plants which 

 have a high rate of respiration also have a high rate of carbohydrate 

 formation. Similar results have also been obtained by Spoehr and 



McGee."' 



Kny^®" has shown that photosynthesis soon ceases when the chloro- 

 plasts are separated from the cytoplasm of the cell, although there appears 

 to be no direct parallelism between injury to the cytoplasm and photo- 

 synthetic inhibition. Disorganization of the cell nucleus is not detrimental 

 to photosynthetic activity. 



Ewart^'*' has also made observations on photosynthesis as affected 

 by an atmosphere of hydrogen and carbon dioxide. Even in mosses, 

 which show this effect more slowly than other plants, stoppage of photo- 

 synthesis finally follows exposure to such an atmosphere. When oxygen 

 is made available the plants recover their photosynthetic ability if they 

 have not been kept in the mixture of hydrogen and carbon dioxide too long. 



^"Plester, Beit. Biol, dcr Pnanzcn., 11, 249 (1912) _ . • », tt- 



'**Henrici "Chlorophyllgehalt und Kohlensaure-Assimilation bei Alpen-hben- 



pflanzen," Inaug. Diss., Basel, 1918, P- 90. 



'^^Boysen-Jensen, 5ofam5^ r((fj.y<tn/i, 36, 219 (1918). 



^"Spoehr and McGee, Carnegie Inst, of Wash. Pub. No. 325, 76-98 (1923). 



>" Kny, Ber. bot. Ges., 15, 388 (1897). 



""Ewart, Linnean Soc, 31, 403 (1897). 



