312 THE CHLOROPHYLLS AxND THE CAROTINOIDS 



nection it may be significant that the hemin of the blood, which is chemically 

 similar in many respects to chlorophyll is bound up with the protein globin, 

 forming hemoglobin. 



A more extreme viewpoint is adopted by Lubimenko (1926, 1927, 1928) 

 who regards the pigment of the chloroplast to be a complex molecule which 

 is built up of the chlorophylls, carotinoids, and protein. According to this 

 hypothesis the pigments ordinarily extracted from green leaves do not occur 

 in the free state in the chloroplasts but result from the decomposition of a 

 complex type of pigment molecule during the extraction process. 



Chlorophyll Synthesis. — Chlorophyll, in common with practically all 

 the other organic substances which occur in plants, is a product of the syn- 

 thetic activities of the plant. A number of conditions are known to be neces- 

 sary for or at least to greatly influence the synthesis of chlorophyll in plants. 

 Absence of any one of these factors will inhibit chlorophyll synthesis resulting 

 in the condition often called chlorosis. This term is most frequently applied 

 when the failure of chlorophyll to develop is due to a deficiency of one of the 

 essential mineral elements. Different types of chlorosis may develop in the 

 leaves of any species depending upon the factor limiting chlorophyll formation. 

 The factors influencing chloroph341 synthesis will be discussed briefly. 



1. Genetic Factors.- — That genetic factors are necessary for the develop- 

 ment of chlorophyll is shown by the behavior of some varieties of maize in 

 which a certain proportion of the seedlings produced cannot synthesize 

 chlorophyll, even if all environmental conditions are favorable for its forma- 

 tion. As soon as the food stored in the seed is exhausted such "albino" 

 seedlings die. This trait is inherited in such strains of maize as a Mendelian 

 recessive and hence is apparent only in plants homozygous for this factor. 



2. Light. — Light is usually necessary for the development of chlorophyll 

 in the angiosperms. In the algae, mosses, ferns, and conifers, however, 

 chlorophyll synthesis can occur in the dark as well as in the light, although 

 the quantity produced is often less in the absence of light than in its presence. 

 In a few angiosperms such as seedlings of the water lotus (Nelu/nbo), and 

 in the cotyledons of citrus fruits chlorophyll can also develop in the absence 

 of light. 



Relatively low intensities of light are generally effective in inducing 

 chlorophyll synthesis in those species in which light is required for this process. 

 All wave lengths of the visible spectrum will, if their energ^^ value is adequate, 

 cause chlorophyll development in etiolated seedlings (chlorophyll-free seed- 

 lings which have been grown in the dark) except those longer than 680 ?ii[i 

 (Sayre, 1928). 



It is quite generally considered that chlorophyll is synthesized in the plant 



