RADIATION AND ANTHOCYANIN PIGMENTS 1111 



(25, pages 83-86) discussed critically the older literature which presents 

 the evidence that carbohydrate and especially sugar accumulation in 

 plants induce pigment formation. Later papers by Sando (29), Emerson 

 (12), Magness (20), Fletcher (13), and others present further evidence 

 of a similar nature or assume that pigment production is increased by 

 the accumulation of the products of photosynthesis. It should be pointed 

 out, however, that the citation of a number of cases where high car- 

 bohydrate content accompanies pigment formation does not prove that 

 such an accumulation causes pigment production. The fact that each 

 molecule of anthocyanin contains normally one or two molecules of sugar 

 makes the above cause and effect relation seem logical, from a chemical 

 point of view. We should not lose sight of the fact, however, that we 

 are dealing with living cells where sometimes reactions take place which 

 are not at all logical from a chemical point of view, and conversely 

 where reactions may not take place although all necessary products are 

 present. When it is recalled that the anthocyanin in any plant probably 

 represents only a very small fraction of the dry weight of the entire 

 plant as compared with 10 to 20 per cent of easily available carbohydrate, 

 any limitation of pigment formation due to a shortage of carbohydrate 

 is unlikely. Although Willstatter and Mallison (35, page 153) have 

 shown that the most highly pigmented part of a dark-red dahlia flower 

 may contain as high as 30 per cent pigment on a dry-weight basis, this 

 localized area contains only a small fraction of the total available car- 

 bohydrate content of the plant. Such high concentrations of pigment 

 even in localized areas appear exceptional in plant tissues. Most of the 

 pigment concentration values given by Willstatter and Mallison for other 

 highly colored flower parts are less than 10 per cent of the dry weight. 

 In many fruits, stems, and leaves where pigment is present only in the 

 first few layers of cells beneath the epidermis the concentration is no 

 doubt only a small fraction of this In contrast with the accumulation- 

 of-products theory as a cause for pigment formation. Combes (9) and 

 Combes and Kohler (10) found a decrease in both nitrogen and car- 

 bohydrate fractions in leaves during the autumnal development of 

 pigment. Murneek and Logan (24) reviewed the literature on the subject 

 and studied the migration of both nitrogen and carbohydrate from several 

 varieties of apple leaves. They found that nitrogen decreases from the 

 time active growth ceases until complete defoliation occurs, but there 

 was no definite trend established in the migration of carbohydrates from 

 the foliage. Denny (11) by means of the twin-leaf method made a careful 

 study of the trends of both carbohydrate and nitrogen fractions in 

 Viburnum and lilac. He found a definite decrease only in nitrogen 

 and that only in the case of Viburnum. No trend was established for 

 nitrogen in lilac leaves or for carbohydrates in either species during the 

 autumn-migration period. Of the two species only Viburnum showed 



