146 



PHOTOSYNTHESIS 



etiolated and chlorotic plants. The conditions under which the experi- 

 ments were carried out were such that neither temperature, carbon 

 dioxide-concentration nor light intensity were determining the rate of 

 photosynthesis. This is, of course, necessary in order to emphasize or 

 demonstrate the influence of other factors, in the cases studied, more 

 especially chlorophyll-content. In most of the experiments excised leaves 



were used. 



Willstatter and Stoll introduced as a measure of the ratio of chlorophyll- 

 content to rate of photosynthesis the term "Assimilationszahl" or photo- 

 synthetic number. This is a measure of maximal photosynthesis expressed 

 in grams of CO2 absorbed per hour by a leaf mass containing 1 gram 

 of chlorophyll under favorable conditions of temperature. Or briefly it is 

 grams of carbon dioxide absorbed per hour i:>er gram of chlorophyll; 

 this is the photosynthetic number which for the sake of brevity we shall 

 designate by Pc- 



hourly photosynthesis, grams COo 



P.= 



grams chlorophyll. 



This term expresses the highest possible rate of photosynthesis under 

 the particular conditions of temperature and carbon dioxide-concentra- 



TABLE 24 



Photosynthetic Number, Pc, of Various 

 Lux, Determined by VV 



Species Temp. 



Aesculus Hippocastanum 25 



Acer Negundo ^^ 



Acer Pseudoplatanus j^ 



Ampelopsis quinquefolia 25 



Hostia plantaginea 3U 



Hydrangia opulodes 30 



Pelargonium zonale ^^ 



Primula ^^^ 



Prunus Laurocerasus ■^ 



Rubus ^^o 



Sambuscus nigra ^^^ 



Tilia cordata j^ 



Ulmus ^^ 



Cucurbita Pepo 25 



Clerodendron trichotomum 



Thumb 25 



Fragaria vesca j-^^ 



Helianthus annuus 25 



'.'.'.'.'.'.'.'...■■ 25° 



Populus pyramidalis hort 25° 



Pelargonium peltatum (from 



green-house) ^^ 



Plants, 5 Per Cent CO2, About 



ILLSTATTER AND StOLL. 



From 10 g. 

 Fresh Leaves : 

 Dry Chloro- 



Weight phyll 



Grams Mg. 



48,000 



2.94 

 2.22 

 3.58 

 2.00 

 1.00 

 1.21 

 0.96 

 0.90 

 3.40 

 3.60 

 2.75 

 3.19 

 2.94 



1.3 



2.07 

 3.00 

 1.72 

 1.94 

 1.67 

 3.19 



.60 



Photosynthesis : 

 gram COjper 

 Hour, per 1 g. 



Dry Weight Pc 



24.7 0.054 6.4 



24.8 0.086 7.7 

 40.0 0.058 5.2 

 28.8 0.089 6.2 



10.0 0.088 8.8 

 9.2 0.050 6.5 



12.5 0.097 7.4 



11.4 0.117 9.1 



12.2 0.029 8.1 



32.4 0.052 5.8 

 22.2 0.034 6.6 



28.1 0.028 6.6 



16.2 0.022 6.9 



17.5 0.164 12.1 



15.0 0.089 12.3 



17.7 0.078 10.6 

 16.5 0.134 14.0 

 15.0 0.129 16.7 



20.8 0.137 10.9 

 19.0 0.060 10.0 



8.2 0.198 14.5 



