Biological Papers. 103 



upper side. Here the grains were few. The third, which had been 

 treated on both sides, had no starch. 



The cocoa-butter was applied by warming it slightly and spread- 

 ing it in a thin film over the leaf, so as to exclude all carbon dioxide 

 gas. This experiment was performed several times, with the same 

 results. 



To be sure the light was not excluded by the cocoa-butter, an 

 experiment was made in the same way by sealing a leaf which con- 

 tained no starch between two one-inch cover-glasses. The sealing 

 was done by fastening the edges of the cover-glasses together with 

 cocoa-butter or salve, the butter coming in contact with the leaf at 

 the petiole only. Thus all carbon dioxide gas was excluded, but 

 the light had free access. After a few hours, starch was found in 

 the other leaves of the plant but none in those so treated. 



On April 12 other leaves without any starch, while yet on the 

 plant, were placed between two squares of dark paper held in place 

 by clasps. Thus light was excluded but air was not. The squares 

 of paper were not as large as the leaf ; so part of it was exposed to 

 the light. When examined, starch was found only in the part ex- 

 posed to the light. The part of the leaf under the black paper had 

 no starch. 



On April 29, at six o'clock p. M., some leaves which were full of 

 starch were treated as above with cocoa-butter — some dorsal only, 

 some ventral only, some on both sides ; hence, in the latter case, 

 all light was excluded. The next morning all the starch had gone 

 out of all the leaves excepting those treated on both sides. These 

 were full of starch. 



On May 2 branches with the leaves full of starch were broken 

 off and placed, at six o'clock p. m., in dark drawers. After sixteen 

 hours the starch had gone from all the cells of the leaves excepting 

 a few of the palisades. Parts of leaves treated in the same way 

 did not lose their starch. 



Hence, when air only was present, the starch went out of the 

 leaf, but only when light and air both were present was starch 

 formed 



A number of experimnts were performed to determine how long 

 it required, when conditions were favorable, for the plant to form 

 starch. 



With the temperature at 20 deg. C, and light readings, red 19, 

 yellow 20, green 20, blue 53.06, starch formed in one hour and 

 thirty minutes. With the temperature 19 deg. C, light readings. 



