THE LIGHT FACTOR IN PHOTOSYNTHESIS 1019 



it must be regarded in the liglit of an iuterinediatc product v,hieii never 

 accumulates to any great extent and itself arises from some other related 

 compound. Noack and Kiessling (85) prepared sufficient quantities of 

 protochlorophyll from the inner coats of the seeds of certain Cucwbitaceae 

 to carry out physical and chemical investigations on it. The absorption 

 bands of protochlorophyll in ether solution are reported by Scharfnagel 

 (98) as follows: I. 6300 to 6150 A, II. 6080 to 5950 A, III. 5790 to 5600 A, 

 IV. 5300 to 5200 A and in the following order of intensity: I, IV, III, II. 

 The emission spectrum of the red fluorescence of protochlorophyll is 



o 



shifted toward the violet: fluorescence of chlorophyll, 6850 to 6280 A, of 

 protochlorophyll 6570 to 6190 A. 



Through a series of chemical investigations Noack and Kiessling have 

 established a relationship between protochlorophyll and chlorophyll a. 

 They conclude that the latter is a product of photooxidation of the former. 

 They found no evidence of two protochlorophylls corresponding to the 

 a and h modification of chlorophyll. That the oxidation of protochloro- 

 phyll to chlorophyll occurs in the living leaves and not in leaves which 

 have been killed was shown by Scharfnagel (98) who also found some 

 indications that with illumination of high intensity the amount of chloro- 

 phyll formed from protochlorophyll is less than with light of moderate 

 intensity. 



o 



By using the first appearance of the X6650 A absorption band of 

 chlorophyll as a criterion for the beginning of chlorophyll formation in 

 etiolated Zea Mays seedlings, exposed to light passing through an assort- 

 ment of filters, Schmidt (100) determined the influence of different wave- 

 lengths. Measurements were made of the time of exposure required for 

 the first appearance of chlorophyll and these times were then calculated 

 on the basis of equal intensities for the different filters. Maximum 



o 



chlorophyll formation was found to occur in the orange, X7100 to 6100 A, 

 but falling off toward the red end of the spectrum ; a minimum was found 

 in the green and a secondary maximum in the blue. Light which had 

 been filtered through an alcoholic chlorophyll solution was ineffective in 

 producing chlorophyll. The superior effectiveness of the red rays is 

 also shown in the investigations of Sayre (96) who, however, simply 

 compared the relative greenness of the experimental plants with controls 

 grown under all wave-lengths of light. From this work, in which light 

 filters were used which, of course, do not yield monochromatic light, it 

 would appear that the limit for chlorophyll formation in the red end of 

 the spectrum is X6800 A. 



Attempts to determine the influence of light on chlorophyll accumula- 

 tion under controlled environmental conditions have served to demon- 

 strate the complexity of this reaction. They tend to confirm the 

 conclusion formulated by Lubimenko (70), that maximum chlorophyll 



