CHLOROPHYLLS A AND B AND THEIR RATIO 403 



different kinds of chlorophyll may be prepared from different species. 

 Willstatter and Stoll obtained their proof with extracted chlorophylls, and 

 thus left the possibility open that different chlorophyll-bearing colloidal 

 systems may exist in various species (c/. Chapter 14, page 388). 



Strain and Manning (1942) found, in the chromatograms of extracts 

 from the higher green plants and algae, "companion bands" to the 

 bands of chlorophylls a and h, which they attributed to two new isomeric 

 forms, a' and h' . Their spectra were very similar to those of the ordinary 

 forms a and h, and they appeared to be reversibly convertible into the 

 "old" chlorophylls. In a propanol solution at 95-100° C, 80% of the 

 old isomers were in an apparent equilibrium with 20% of the new ones. 

 Rapid extraction at low temperature (— 80° C.) gave no trace of isomers 

 a' and h' ; it is thus possible that they do not exist as such in nature, but 

 are formed from a and 6 during the extraction at ordinary temperature. 

 On the other hand, the ease with which the old isomers could be converted 

 into the new ones in vitro argues for their presence in the living plants, 

 particularly at the higher temperatures. 



Inman and Blakeslee (1938) found that the absorption spectrum of 

 the chlorophyll extract from an x-ray mutant of Datura was different 

 from that of ordinary chlorophyll. Apart from this isolated observation, 

 the chlorophyll of all investigated higher land 'plants has been found to 

 consist of the same two components — the blue-green component a and 

 the yellow-green component h. As shown by table 15.1 (page 409), the 

 ratio of [a]: [b] is remarkably constant, varying for most normal leaves 

 between 2.5 and 3.5. Limited, but systematic changes in this ratio 

 have been related by Seybold and Egle (1937, 1938) to the "Hght field" 

 to w^hich individual plants were exposed during growth, or to which 

 the species as a whole has become adapted. The proportion of chloro- 

 phyll h is larger in "shade plants" than in "sun plants." Most green 

 algae behave as extreme shade plants, with the average ratio of [a] : [b] 

 going down to 1.4, while alpine plants represent the extreme sun type, 

 with the average ratio of [a]:[b] rising to 5.5 {cj. pages 422-424 and 

 Table 15. VIII, page 423). An abnormally large ratio (about 7) of 

 [a]:[b] was found in the chlorophyll-deficient aurea leaves (c/. Seybold 

 and Egle 1938). 



More recently, Seybold (1941) suggested that the most important 

 factor in the determination of the ratio [a] : [b] is the intensity of 

 primary starch synthesis, rather than light adaptation. This new 

 hypothesis was based on less extensive experimental material than the 

 older adaptation theory (c/. page 422). Seybold's assumption that 

 chlorophyll 6 is a specific sensitizer for the polymerization of sugars to 

 starch (rather than for photosynthesis proper) appears highly improbable. 

 Whether the correlation of chlorophyll 6 content with starch production 



