282 BOTANICAL GAZETTE [APRIL 
than plants grown in the open; but this experiment is open to 
several objections, not the least of which is that only the leaves 
were taken into consideration. 
TscHAPLOwI1z, who gave considerable attention to the effect 
of transpiration on production, found in many of his experiments 
an increased production of dry substance as the result of decreased 
transpiration. From a consideration of these results in connection 
with those of others,* who according to him have found that an 
excessive depression of transpiration results in a lowering of assimi- 
latory activity, he was led to the conclusion that there exists for 
plants an optimum magnitude of transpiration; and that if the 
transpiration exceeds, provided the turgor is always maintained, or 
falls short of the optimum, it is not possible for the plant to reach 
the maximum production of which it is innately capable. He 
regards transpiration as essentially a physical process, the magni- 
tude of which may vary within wide limits without seriously dis- 
turbing the character of the processes in the plant, although there 
may be marked effects on the quantitative results of these processes, 
that is, on the quantity of the assimilatory products formed. 
More decisive are the results of WoLLNy,?’ who grew plants of 
barley, vetch, alfalfa, flax, and potato under conditions giving three 
degrees of humidity, and found that with an increase in the degree 
of humidity there was an increase in the production both of the 
absolute quantity of fresh material and of dry matter. These 
experiments seem to indicate that a depression of transpiration 
results in an increase in the assimilatory activity of the plants. 
In the experiments reported in this paper, the plants growing 
in the open transpired about 10 liters per plant or nearly 30 per cent 
more water than those grown under shade, yet in spite of this differ- 
*s TscHapLtowitz, F., Uber den Einfluss der a des Zuwachses un 
der Temperature auf die Verdunstung der Pflanz Wiener Obst- und Garten- 
Zeitung 2:127-132, 169-175, 222-228. 1877; Landw. enw -Stat. 23:74. _ gen 
of address without title); Unters. i. d. Einwirkun wad deg e u.d. a. Formen d. Natur 
rar a. ae pOptinvant? ‘Bot, Ze qt pp. Leipzig, — cit ee = 
Transpira ons-Optim is ot. Zeit. 4t: 352-362. “1883; Berrien neg, TT a 
Gesamt | Gebiet Agrikultur-Physik. 9:117-145. 1886. 
4 The authorities are not given 
2s WoLLNY, W., Viticenchinees iiber den Einfluss der Luftfeuchtigkeit auf das 
W: um der Pflanzen. Tnaug. Diss. Halle. 1898. 
