EFFECT OF SHADE OX THE THICKNESS OF LEAVES. 2o 



The potato leaf prints present a very uniform gradation, being 

 lightest in the case of leaves produced under full light and darkest in 

 those produced under the deepest shade. (PI. Ill, fig. 1.) In the older 

 leaves a marked difference was noted between those produced under 

 light intensities of n 2 and no. The prints from leaves under n 2 

 were almost as white as those grown under full light, while those in 

 n/o were almost as dark as from the leaves grown in n 7 or below, 

 which shows a comparatively great morphological variation as a 

 result of changed conditions. 



In cotton (PL V. fig. 1) there was a rather uniform gradation in 

 darkness of the print, passing from full light to the deeper shade-. 

 The most marked difference occurred between normal (section 6) 

 and n 2 (section 5 1 light. In the cotyledons this difference is not so 

 marked as in the later leaves, but there is a great although gradual 

 variation from n 93 to normal illumuiation. Cotton showed consid- 

 erable morphological differences in both the cotyledons and the foliage 

 leaves. 



Mustard shows a very gradual although slight cliff erence in the 

 leaves in passing from n 93 to normal light. (PI. IV. fig. 2.; This 

 indicates but little ability to modify the leaf morphology to meet 

 changed conditions. 



Radish shows a marked difference in the leaves produced under 

 normal light as compared with those developed under n 2 and corre- 

 sponding differences under each deeper shade. (PL V, fig. 2.) The 

 same is true of lettuce. (PI. IV, fig. 1.) In each case profound mor- 

 phological changes resulted from altered environmental conditions. 



It is especially interesting to note that the leaf prints for a number 

 of these plants indicate marked morphological differences such as 

 have been noted in comparing sun and shade leaves of the same spe- 

 cies (Stahl. 1883). Two of the plants used, corn and mustard, show 

 little variation, and these plants are the ones which have proved the- 

 least productive in shade. All of the others — cotton, potato, radish, 

 and lettuce — show pronounced variations or morphological adapta- 

 tions, and these are the plants which have shown increased produc- 

 tion when grown in shade. 



GENERAL DISCUSSION. 



Lubimenko (1908) showed clearly that in France a slight reduction 

 of illumination produced an increase in the production of dry matter 

 in the great majority of the plants tested. Shades giving only a 

 slight reduction of light intensity were employed, and no attempt 

 was made to equalize other conditions. The work of Combes (1910) 

 is far more exhaustive and brings out the fact that some of the plants 



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