7S PLANT PHYSIOLOGY AND ECOLOGY 



is made to obtain the light intensity at the time. The epidermis 

 print, as it is called, is compared with the standard, using the 

 second exposure as a check upon the latter. A leaf print is made 

 in similar fashion and at the same time by placing the leaf closely 

 over the opening. The value of the epidermis print less that of 



Fig. 21. A leaf print of the sun and shade leaves of four species which 

 show both sun and shade fonus. or varieties. In each the shade leaf 

 is the darker. 



the leaf print is a measure of the absorption of the chlorenchym, i.e., 

 of that part of the leaf sensitive to light. In the sunflower the 

 value of the epidermis print is .1 approximately, that of the leaf 

 print .003, and the light absorbed by the leaf is consequently .097. 



Experiment 22. Epidermis and leaf prints. Strip from the upper 

 surface of a sunflower leaf a piece of epidermis sufficient to cover the 

 opening of the photometer. ]\Iake an exposure beneath the strip, and 

 with the same or a similar leaf make a leaf print. Take a third reading 

 to obtain the full light intensity. Compare the results with the standard, 

 and determine the amount of light screened out by the epidermis, 

 absorbed by the chlorenchym, and transmitted through the entire leaf. 



