714 



William F. Prickett, F. Dudley Bryant, and Paul Latimer 



about 0.3. Hence this approximate type of theoretical approach is quantitative- 

 ly inadequate for these chloroplasts in the red region in contrast to the finding 

 for red blood cells'^' in the blue spectral region. The present failure is prob- 

 ably because of the low ratio of particle size to wavelength and the neglected 

 effects of internal particle structure. 



This finding differs from that of Charney and Brackett'^' who obtained 

 surprisingly good agreement between the predictions of similar equations and 

 experiment. Part of the reason for this disagreement lies in the assumed ef- 

 fects of suspension attenuation on the shape of the scattering spectrum. Their 



Fig. 2. Spinach chloroplast: 

 scattering cross section (Sp), 

 experimental and theoretical. 

 Ordinate scale is absolute for 

 theoretical curves. Experi- 

 mental curve was multiplied by 

 5. 4 for plotting convenience. 

 Theoretical curves are based 

 on one, two, and three band 

 models of chlorophyll a system. 



X(fT^) 



correction for attenuation greatly enhances the ratio: maximum to minimum 

 values on the theoretical scattering curve. While it appears to have been ap- 

 propriate in accounting for their experimental data, no correction for such 

 effects was made on our theoretical curve since the experimental method in 

 principle yields curves which are corrected for the attenuation. In addition, 

 it should be noted that our recent studies of single partial layers of similar 

 chloroplasts gave experimental scattering curves with a somewhat greater 

 ratio of maximum to minimum than is seen on the above experimental curve. 

 Because of the similarity of particle parameters, the theoretical curves for 

 these latter chloroplasts should be similar to that given above. Since it is 

 clear that no attenuation correction is appropriate in this case, this confirms 

 that the experimental scattering curve in Fig. 2 is representative of particle 

 characteristics unmodified by distorting influences. Thus it is appropriate to 

 compare this with theoretical predictions of particle characteristics. 



However, despite this limitation of these theoretical curves, which depend 

 on assumed absorption band structure, further examination suggests that 

 measurements of scattered light may be capable of providing information about 



