Iß Bouyoucos, Transpiration of Wheat Seedlings as Affected etc. 
once suggest tbe metbod already described of determining tbe 
concentration of the soil solntion. Wbetber it would be a practical 
way, bowever, is another question. 
Tbis, in sbort, is the manner in wbicb tbe osmotic pressure 
of tbe solution and tbe density of tbe cell sap may cause tbe re¬ 
lative transpiration to increase witb tbe decrease in density of tbe 
solution down to a certain point. Tbe decrease of tbe correlative 
transpiration from tbis point down, i. e., witb tbe furtber decrease 
in density of solution, may be attributed to anotber factor, namely, 
to tbe decreased power of certain densities of solution to stimulate 
transpiration. It is assumed bere tbat tbe lowest density of tbe 
nutrient solution bas a sligbt stimulative action upon transpiration, 
and tbat it increases witb tbe increase in concentration up to a 
certain point, beyond wbicb it ceases, or is overcome by tbe os¬ 
motic pressure; or dccreases from tbis point witb tbe diminution 
in density, just as bas already been noted. In otber words, tbe 
decreased transpiration per unit of growtb from tbe intermediate 
to tbe most dilute solution, is ascribed to tbe reduced stimulative 
action of tbe decreased density of solution. To state tbe same 
tbing in tbe converse form, tbe rise in tbe relative transpiration 
from tbe most dilute to tbe intermediate densities, is due to tbe 
greater stimulative action of tbe increased concentration. Tbe 
stimulative action cannot continue mucb furtber upward tban wbere 
tbe change in tbe curve occurs, because it eitber reacbes its 
maximum, or it is overcome by otber factors, namely, tbe osmotic 
pressure of tbe solution, and tbe different pbysical properties of 
tbe cell sap. 
In wbat manner tbe transpiration is stimulated or accelerated 
by tbe dilute Solutions is not known, it may be cbemical, pbysio- 
logical or botb. 
Tbe wbole problem may now be stated in eitber of tbe 
following ways: 1) tbe transpiration per unit of growtb increases 
witb tbe increase in density of solution, due to tbe stimulative 
action of tbe latter, until a certain concentration is reacbed and 
tben begins to decrease witb a furtber rise in density, due to tbe 
increased osmotic pressure of tbe latter and to tbe increased density 
of tbe cell sap; or 2) tbe relative transpiration increases witb tbe 
decrease in concentration down to a certain point, due to tbe re¬ 
duced osmotic pressure of tbe dimisbed densities of solution and 
to tbe decreased power of tbe cell sap to reduce evaporation, and 
tben it begins to decrease witb a furtber decline in density, due 
to tbe reduced stimulative action of tbe latter upon it. 
Going back to tbe original tables (I—III) of solution, sand, and 
soil cultures, it is very siguificant to note tbat wbile tbe relative 
transpiration increases down to a certain point and tben decreases, 
tbe total dry matter produced increases in all tbree cultures witb 
tbe rise in density. In otber words, tbe actual plant growtb is 
proportional to tbe concentration of tbe solution. -Tbis ratio is 
certainly remarkable for its regularity, being perfectly constant 
witbout any interruption in tbe curve from tbe lowest to tbe hig- 
best density in all tbree cultures. 
