THE CHLOROPLAST PIGMENTS 



479 



plant syntheses are dependent upon solar 

 energy it appeared desirable to find out 

 whether or not the production of vitamine 

 A is dependent upon photosynthesis. 

 His experiments have led him to conclude 

 that photosynthesis is not necessary for 

 the production of vitamine A in plants, for 

 wheat sprouts grown in either the dark or 

 the light seemed to be adequate sources 

 of vitamine A. The green sprouts appar- 

 ently were more active than the etiolated 

 ones . 



On the other hand, Coward has found 

 that light is necessary for the formation of 

 vitamine A in plant tissues. An investi- 

 gation of some of her results on the effect 

 of carbon dioxide, oxygen and chloroform 

 shows that much more work is necessary 

 before any conclusion can be drawn 

 regarding these factors. 



It is reasonable to conclude, say Coward 

 and Drummond, that the formation of the 

 large amounts of vitamine A found in the 

 green leaves of most plants demands the 

 influence of light. 



On the other hand the carrot and the 

 sweet potato are examples showing that 

 vitamines may be present in tissues which 

 are not exposed to sunlight. It has been 

 questioned whether the vitamine has 

 been formed in the root of the carrot or 

 whether it has been transported there 

 from the leaves, where it is definitely 

 known to occur. Coward has shown that 

 the vitamines and carotin can be trans- 

 ferred upward from the carrot to its 

 leaves, and there is no reason to believe 

 that the reverse process can not take 

 place. 



Coward and Drummond believe that the 

 fat soluble vitamine occurs in the green 

 actively assimilating parts of plant tissue 

 and that it is generally absent from the 

 localities where chlorophyll is not found. 

 Lower organisms devoid of chlorophyll do 

 not seem to synthesize vitamine A. It is 



known also that the outer green leaves of 

 cabbage contain more vitamine A than the 

 white inner leaves. 



The common green seaweeds contain as 

 much vitamine A as do green land plants 

 such as cabbage. It is believed that this 

 is not present in the form of a complex 

 with protein in green leaves . Vitamine A 

 can be extracted from green leaves by fat 

 solvents and can also be obtained in the 

 unsaponifiable fraction of the fatty sub- 

 stances extracted from green leaves. 



Coward says that its absence from 

 etiolated leaves, or those which have 

 never been exposed to the light, has been 

 shown and likewise its presence in all 

 plant tissues so far examined which 

 contain lipochromes and which have also 

 been exposed to the light. In the case of 

 underground structures, the only ones 

 found to contain more than the merest 

 trace are the carrot and the yellow sweet 

 potato, each of these also containing lipo- 

 chromes. Comparisons between different 

 green vegetables or salads have sometimes 

 been made regarding the vitamine content, 

 but apparently very little consideration 

 has been paid to the possible differences of 

 vitamine content of leaves of the same 

 plant grown or preserved under different 

 conditions. Attention has been called to 

 the difference in the vitamine content of 

 two different samples of hay, but the 

 difference was ascribed to the method of 

 curing rather than to a difference in the 

 hay on cutting. Some have noted a very 

 marked difference in the vitamine A con- 

 tent of butters made from the milk of 

 cows fed at the beginning of the experi- 

 ment on a sample of hay which had been 

 cut when growing vigorously and later 

 on hay which had been cut when it was 

 beginning to wither. The difference in 

 the butters has been shown to have been 

 due to the difference in the vitamine 

 content of the two samples of hay by 



