EFFECTS OF HIGH-INTENSITY IRRADIATION 



121 



approaches the shape of the sixth leaf and not that of the twelfth. A 

 few leaves of a relatively high length breadth relation are then 

 produced, after which decrease of length/breadth again is observed, 

 the curve is fairly parallel to that of the original set of the sixth to the 

 twelfth, and, at about the twenty-fourth leaf, the curve is again more 

 or less on the level of the twelfth leaf. The effect of defoliation 

 indicates the existence of a correlative connection between the various 

 leaves. We will presently see another example of such a correlation. 

 As stated above, the effects of yellow and of blue light on leaf 

 shape in lettuce are related as are those of lower and higher light 

 intensities. In each spectral region, moreover, a light intensity de- 

 pendence of leaf shape is clear (Fig. 6). The figure shows that a plant 

 at 11,000 ergs/cm- sec in yellow light is much more elongated than 

 one at 10,000 ergs/cm- sec in blue light (var. Meikoningin ) . 



50.000 26. OC^ 10,000 



Bum LIGHT (ergs/offi^/seo.) 



50.000 27.000 11.000 



YgLLOW LIGHT {ergg/om^/seo. ) 



Fig. 6. Lettuce, var. Meikoningin, grown in either exclusively blue light 

 or exclusively yellow light, both at three different intensities. Photographed 

 July 21, 1955. 



