C. STACY FRENCH 



71 



follows the same type of excitation curve, except that these two drop 

 to a low minimum at about 435 m/x. It therefore appears in agreement 

 with Duysens (1952) that phycoerythrin absorbs energy and transfers 

 it to the phycocyanin which passes it along to chlorophyll. Presumably 

 this same process may be followed by the energy used for photo- 

 synthesis, although this conclusion of course involves several assump- 

 tions. 



The effect of the intensity incident on a red alga upon the shape of 

 the fluorescence curve is shown in Fig. 21. These curves were meas- 



I I 



-I — 1 — I I I — I — I I ' I I ' ' — r- 



LOW INCIDENT - 

 INTENSITY 



. u ^-^j . 



I ^^ I I 



'DIFFERENCE ^^^ ^ 



/'between low and HIGfi- 

 ' INTENSITY CURVES 



J 1 1 J I — 1 — 1 — I — 1- 



600 650 700 



WAVE LENGTH IN MJJ 



750 



Fig. 21. Fluorescence spectra of a red alga after illumination for 6 minutes with 

 three different intensities. Only the chlorophyll peak is reduced in height 

 by prolonged illumination at high intensity. (French and Young, 1952.) 



ured, as were all the others in this article, after the initial changes of 

 intensity of fluorescence, the Kautsky effect, had come to completion, 

 so that constant readings were obtained. These changes are connected 

 with the induction period of photosynthesis. A great deal of specula- 

 tion has been aroused by observations of these phenomena. Here we 

 see that low intensity gives far more chlorophyll fluorescence in pro- 

 portion to that of phycoerythrin and phycocyanin than do higher 

 intensities. This is another manifestation of the Kautsky effect. Here 



