399 



T. T. Bannister and M. J. Vrooman 



enhancement. However, as Myers (3) has pointed out to us, dif- 

 ferent maximum limits to enhancement are predicted by the two 

 models. Thus, for the spill-over model, the ratio of (p-^^g'Pl)/?? 

 could not exceed 2.0 (assuming equal rates of both photoreactions), 

 whereas higher values would occur with the separate package hy- 

 pothesis; thus, the formulations promise to be helpful in dis- 

 criminating experimentally between the two models. 



Thirdly, the formulations give a ready explanation to some 

 previous observations. For example, the increase in maximum E, 

 and the increase in the ratio P-i/p^ required to obtain maximum E, 

 which Myers and Graham (4) reported to attend increasing wave- 

 length of far-red, are predicted (equations (9) and (ll), or (9a) 

 and (lla) ), assuming a declines with increasing wavelength. 

 Myers and Graham also found that the slopes of curves representing 

 E(p, ), for pp constant, in the region of small P]_, were independent 

 of rar-red wavelength. This agrees with equations (7) and (Ta), 

 which show the slope depends only on b. 



Finally, our analyses suggest that, aside from the discontin- 

 uity discussed above, the general semiquantitative dependence of 

 enhancement on illuminations can be explained on the basis of 

 either model, provided saturation is taJten into account. Con- 

 versely, our findings indicate that saturation must generally be 

 reckoned with, even at low illuminations normally regarded as 

 within the linear portion of an illumination curve. For example, 

 in determining a maximum value of E, care must be taken that Pj^ 

 not be much in excess of that value just giving maximum E; other- 

 wise a less thaji maximum value of E will be obtained. 



This work was supported by the National Science Foundation. 



REFERENCES 



1. Myers, J. ajid J. Graham. Plant Physiol. 3S: 1-5- 1963* 



2. Bannister, T. T. and M. J. Vrooman. Manuscript in preparation. 



3. Myers, J. Personal communication. 



h. Myers, J. and J. Graham. Plant Physiol. 38: IO5-I6. I963. 



