408 



THE PIGMENT SYSTEM 



CHAP. 15 



1939) and Seybold, Egle, and Hiilsbruch (1941). Table 15.1 contains 

 a selection from the results of these investigations. It shows the "nor- 

 mal" concentration of chlorophyll and the "normal" ratio [a]:[b] in 

 plants of different types. Finer differences, which can be interpreted as 

 adaptations to different "light fields," are discussed on pages 422 et seq. 

 Table 15.1 shows that the total chlorophyll content of most leaves — 

 with the exception of aurea varieties — is of the order of 0.7-1.3% of dry 

 weight (Willstatter and Stoll). This average content does not depend 

 on geographical latitude (Lubimenko 1928), although the range of its 



vacuole 



wall 



=^ 



cytoplasm 



chloroplast nucleus 



Fig. 48. — Section through a cell of Elodea, showing the 

 largest part of it occupied by the vacuole (from Robbins and 

 Rickett 1939). (Courtesy of D. Van Nostrand Company, Inc.) 



variations is far larger in the tropics than in moderate zones (cf. page 422) . 

 Contrary to earlier results of Henrici (1919), alpine plants were found 

 by Seybold and Egle (1939) to contain not less total chlorophyll (referred 

 to unit surface) than plants from the lowlands. The only leaves in 

 table 15.1 whose chlorophyll content is a whole order of magnitude 

 smaller than that of all others are those of the aurea variety of the elm; 

 the same was found to be true also for other yellow summer leaves 

 investigated by Willstatter and Stoll. 



6. Chlorophyll Content of Algae 



As shown by table 15.11, earlier investigators (Willstatter and Stoll 

 1913, and Lubimenko 1925) found that algae are less rich in chlorophyll 

 than land leaves. The appearance of such bright-green algae as Ulva 

 laduca does not support this conclusion. Newer studies of Seybold and 

 Egle failed to confirm it; they found the content of most algae in chloro- 

 phyll to be similar to that of green plants, that is, 0.5-1.5% of the dry 

 weight. Unicellular green algae (e. g., Chlorella) may contain up to 

 4 or 5% chlorophyll {cf. below). Seybold and Egle (1938) suggested that 



