The Prevalence of Green Color in Plants 25 



simply state that the result of the test is perfectly conclusive, — it 

 shows that leaves, apart from varying amounts of water they con- 

 tain, always gain weight in the light but not in the dark. They 

 are always heavier in the evening than they were in the morn- 

 ing. As to what becomes of the starch and sugar which disappear 



This square is Jo of a meter (a decimeter) on a side, and fj^ of a meter 

 in area. 



An area of leaf exactly equal to this square would make iJo of a gram 

 of grape sugar in an hour, or ^ of a gram in a day, or 1 gram in 

 10 days, or 15 grams (which is h of an ounce) in a summer. 



This amount of grape sugar made in a summer, viz. 15 grams, would 

 form a cube 2.15 centimeters on a side, the size of the small 

 square in the lower right hand corner of this square. Or, it 

 would form a layer over this entire square 1 millimeter (^V of 

 an inch) thick, the thickness shown by the space between the 

 larger and smaller squares. 



Fig. 3. — Diagram to illustrate the quantity of photosynthate made per unit area 



of leaf. 



from the leaf, that will later be shown, though we may here note 

 in passing that there is a continuous movement of the sugar from 

 the leaves into the stem. Furthermore, this same method en- 

 ables us to establish the amount of the increase in weight. This 

 varies greatly, of course, with different plants and under different 



