1268 



THE PIGMENT FACTOR 



CHAP. 32 



Chlorotic plants, i. e., plants in which the clilorophyll development has 

 been arrested by nutritional deficiencies, also have been investigated by 

 Willstatter and Stoll. The assimilation numbers of plants of Helianthus 

 annuus and Zea mats, made chlorotic by iron deficiency, were found to be 

 not very different from those of normal plants (sometimes smaller, some- 

 times larger). It thus seems that the development of the enzymatic ap- 

 paratus has been held back together with that of chlorophyll. 



100 



to 



> 

 (/) 

 o 



I- 

 o 



I 



Q. 

 li. 

 O 



UJ 



I- 

 < 



0.025 0.050 0.075 0.100 



RELATIVE CHLOROPHYLL CONCENTRATION 



Fig. 32.3. Relation between chlorophjdl concentration and photosynthesis of Chlorella 

 in strong Ught (after Emerson 1929). Two series of experiments. 



These results of Willstatter and Stoll were confirmed and amplified by 

 Emerson (19290, who investigated cultures of Chlorella vulgaris grown in 

 nutrient solutions with a variable concentration of iron. Glucose was 

 added to support growth in iron-deficient solutions. In this way, varia- 

 tions of [Chi] in the ratio 1:5 could be obtained. The maximum photo- 

 synthetic rate (in Warburg's buffer No. 9, and in light of about 10^ lux) was 

 found to increase regularly — but more slowly than proportionately — with 

 the chlorophyll content {cf. fig. 32.3). The high light intensity used by 

 Emerson made it improbable that the increase in P with [Chi] could be in- 

 terpreted as a conseciuence of incomplete light saturation of the chlorophyll- 

 deficient cells; this conclusion was confirmed by a second investigation 

 (1929^), in which complete light curves were determined for two Chlorella 



