No. 2, September, 1921] PHYSIOLOGY 157 



a 

 Q - equal to an average of 2.9 =^ 0.5 — O.G. Under natural conditions this relation is not dis- 



b c 



turbed during photosynthesis. The relation of the 2 carotinoids, Q - = O.GO =*= 0.1, also shows 



X 



but slight variation during photosynthesis. Detailed directions are given for the analytical 



r , , , , 1, rr,. • chlorophyll ^ a+b 



determination of the chlorophyll components. The quotient : — — =Q vanes 



carotinoid c+x 



greatly in different leaves and during the year. In autumn the chlorophyll components de- 



c a 



crease while the carotinoids remain, Q - varies irregularly, but Q - remains about constant. 



X b 



a a+b 

 After long continued photosynthesis, 22 — 67 hours, Q - and Q were but very slightly 



c ° ^^^ 



changed, while Q - was shifted in favor of the xanthophyll. An increase in the rate of res- 



^ a c 



piration by raising the temperature to 30 — 37°C. had no effect on Q - andO - . Photosyn- 



a 

 thesis at 37 — 45°C. had no effect on the chlorophyll content, but Q - was lowered. During 



b 



very active photosynthesis, that is, at 30 — 32°C., 5 percent COj, and light more intense than 

 sunlight, after 6 hours no change in the chlorophyll content was observed. — II. The relation 

 between photo synthetic activity and the chlorophyll content of leaves. The complex apparatus 

 and methods used are described, based upon differential determination of CO 2 absorbed in 

 KOH bulbs and weighed. Cut leaves were used and a metal filament electric lamp as the 

 source of the light. "Assimilationszahl" is taken as a measure of photosynthesis and defined 

 as grams of CO2 fixed per hour per gram of chlorophyll. This varies with the species and 

 with age of leaf used. For 1 molecule of chlorophyll old autumnal leaves of Ampe/opsts quin- 

 quefolia fixed 18 molecules CO2 and young autumnal leaves of the same plant 164 molecules; 

 in the summer, leaves of Sambucus nigra fixed 135 molecules CO2, Sambucus nigra var. aurea 

 2463; etiolated leaves of Phaseolus vulgaris fixed 2736 molecules CO2. Experiments with 

 leaves in early spring indicate that the development of pigments and of the photosynthetic 

 machine are not parallel and it is concluded that photosynthesis is dependent not only upon 

 chlorophyll but also upon an internal factor which precedes chlorophyll in the development 

 of the leaf. When yellow autumnal leaves are brought under experimental conditions of 

 maximal photosynthesis (25°C., 5 per cent CO2, 48,000 M. C. S.) their activity on the basis 

 of chlorophyll content is about the same as the normal leaf, for the activity of the internal 

 factor has been reduced to about the same extent as the chlorophyll content. The "Assimila- 

 tionszahl" of the skins of fruits is about the same as that of leaves. The absolute value of 

 the photosynthetic rate is about the same for normal leaves and leaves of varieties poor in 

 chlorophyll, and in the case of Ulmus, on the basis of leaf area, the leaves low in chlorophyll 

 have the highest rates. With advancing season chlorophyll content increases while rate 

 of photosynthesis decreases. In the yellow varieties the carotinoids are not higher in actual 

 amount but only in proportion to the chlorophyll. That these yellow pigments play no direct 

 role in photosynthesis is shown by the fact that when the violet rays, which are absorbed only 

 by the carotinoids, are removed by means of a potassium bichromate filter, no reduction in 

 the rate was observed. By filtering the light through 1 leaf of Cucurbita pepo, the photo- 

 synthetic rate of the same species was reduced to 1/20 of that without the filter, and filtered 

 through 2 leaves the rate was zero. A comparative study of etiolated and normal leaves 

 showed remarkably high photosynthesis rates for the former. Etiolated leaves exposed to 

 the light (3-48 hours showed rates which in absolute values were higher than those of normal 

 leaves. Etiolated leaves which had developed but 3-6 per cent of the normal chlorophyll 

 content were able to fix completely their respiration C02. Chlorotic leaves exhibit a very 

 weak photosynthetic activity. Anthocyanin seems to be without influence on photosynthe- 

 sis. The parasite Neoitia nidus avis was found to contain chlorophyll, but even at 30°C. 

 and with 5 per cent CO2 it carried on no photosynthesis. A comparative study, with leaves 

 rich and poor in chlorophyll, of the effects of variations in temperature and light intensity 

 revealed a decided disproportionality between chlorophyll content and photosynthetic 



