STUDIf:S IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



91 



No. 



On the other hand, the many claims of simple and complete explana- 

 tion of the process, based usually on very limited and inadequate 

 experimentation, have done more to befog the issues than to clarify 

 them. The factors of carbon-dioxid supply, light intensity, the 

 quantity of chlorophyll, temperature, and water-supply have all 

 received more or less exhaustive treatment. Practically all of these 

 investigations have revealed the fact that there are other internal 

 factors operative. The nature of these internal factors is unques- 

 tionably complex, though there is no reason for supposing that they 

 are not amenable to physical and chemical investigation. 



Table 54. — Rates of respiration and synthesis of an excised bean leaf {Canada Wonder) 

 kept in the dark 64 hours previous. 

 In atmospheric air at the constant rate of the air-stream equal to 0.64 mg. CO2 per 2-hour 

 period. Observations made at 23.8°. Area of leafj = 111.84 sq. cm. Light intensity 7,140 lux. 



Time. 



ai'lS" 

 5'>30'' 



7h45m 



10 p.n 



12»'15" 

 2''30" 



4h45m 



7 a.m 



9h20n) 



llMO" 

 1''55'" 



4h05m 



6''20'° 

 8''35'" 

 10''45" 



Dec. 13: 



p.m. to 5''15™ 



p.m. to 7'^30™ 



p.m. to 9H5"' 



a to 12 n 



Dec. 14: 

 "a.m. to 2'' 1.5" 

 a.m. to 4'>30" 

 a.m. to 6''45" 



. to 9 a.m 



a.m. to ll'^20'» 

 ° a.m. to l'>40" 

 p.m. to 3*^55'" 

 p.m. to 6''05'" 

 p.m. to 8''20°> 

 p.m. to 10'»35™ 

 '»p.m.tol2''45'» 



a.m. 

 p.m 

 p.m 

 p.m 

 p.m 

 p.m 

 a.m 



Dark 

 Do. 

 Do. 

 Do. 



Do. 

 Light 



Do. 



Do. 



Do. 

 Dark 

 Light 



Do. 



Do. 



Do. 

 Dark 



Hrs. 



Total 

 hours. 



66.00 

 68.25 

 70.50 

 72.75 



75.00 

 77.25 

 79.50 

 81.75 

 84.08 

 86.41 

 88.66 

 90.82 

 93.07 

 95.32 

 95.48 



Mg. 

 CO2 

 ab- 

 sorbed. 



1.34 

 1.22 

 1.12 

 0.98 



0.89 

 0.27 

 0.10 

 0.04 

 0.05 

 1.01 

 0.17 

 0.10 

 0.09 

 0.23 

 1.38 



Respira- 

 tion, mg. 



COj 

 emitted. 



0.70 

 0.58 

 0.48 

 0.34 



0.25 



0.37 



Photo- 

 ; synthesis, 

 mg. CO2 

 fixed. . 



0.62 

 0.79 

 0.85 

 0.84 



0.84 

 0.91 

 0.92 

 0.78 



Respira- 

 tion per 

 sq. cm. per 

 hour in 

 mg. CO2. 



0.0063 

 0.0051 

 0.0042 

 0.0033 



0.0022 



0.0034 



0.0066 



Photo- 

 synthesis 



per sq. cm. 



per hour in 

 mg. CO2. 



0054 

 0072 

 0076 

 0076 



0076 

 0080 

 0082 

 0072 



The course of carbon-dioxid emission by leaves as the supply of 

 available carbohydrates diminishes has been described in the first 

 section of this publication. The decrease in the rate of carbon- 

 dioxid emission is a well-known feature of these conditions. How- 

 ever, the course of the photosynthetic process under these circum- 

 stances has received little attention. 



1. In table 53 the results are given of the rates of respiration 

 and subsequent photosynthesis of a bean leaf which had previously 

 been kept in the dark for 64 hours. The carbohydrate supply had 

 thus been very appreciably diminished and the decreasing rate of 

 carbon-dioxid emission is evident. For the experiment atmospheric 

 air was employed and throughout the experiment the temperature 

 of the thermostat was kept at 23.8°. 



