104 Gregory. — The Increase in Area of Leaves and 
of a plant, excluding the weight of reserve material in the seed, results 
almost entirely from the assimilatory activity of the leaf surface, and hence 
the development of the leaf surface must to a large extent determine the 
Fig. 7 . Curve ol increase in total leaf surface, June 1917. Equation of curve of closest fit : 
A — 1 3*76 ^ 0 * 196 1 . 
rate of increase in dry weight of a plant. Considerable work on the rate of 
increase in dry weight, or ‘ Substanzquotienten ’, has been done by 
Kreusler and his co-workers, Gressler, Hackenbei'g, Gericke, and Kiltz, but 
since, except in the case of Kreusler’s work, no data of the rate of increase 
