Dec. 18, 1916 
Influence of Bordeaux Mixture on Transpiration 535 
A study of the last column of Table I brings out the fact that the first 
2-hour period after spraying yielded higher ratio values than the second 
period after spraying. A notable exception to this, however, is the 
experiment with Datura metaloides conducted on March 22. Here the 
second period after spraying yields a ratio value considerably higher 
than the first, while in the experiment with Swiss chard the ratios for 
the two periods after spraying have the same value. The experiments 
with Datura sp. and with castor-bean leaves, extending over time periods 
of four days and five days, respectively, show a decrease in the ratio 
values for the time periods of successive days. It appears, therefore, 
that in these experiments the highest rate of water loss from the leaves 
due solely to the influence of the spray occurred soon after the spray had 
dried upon the leaves, certainly within the first 2-hour period, after 
which there was a gradual decrease in the transpiration rates as influenced 
by the surface film of the spray. As is clearly brought out in the experi¬ 
ment with castor-bean leaves, this gradual decrease in the rates of 
water loss from the leaves, as indicated by the ratio values, extends 
through a period of three days after spraying. The gradual decrease in 
the ratio values during the period after spraying is undoubtedly caused 
by the gradual disintegration and wearing away of the surface films. It 
may therefore be assumed that whatever may be the physical basis for 
the increased evaporation rates from plant surfaces following the appli¬ 
cation of Bordeaux mixture, a modification of leaf structure in response 
to a chemical stimulus induced by the spray can not be responsible for 
the increased transpiration rates. 
In Table II is given a brief summary of the average data presented in 
Table I. The ratio values of total transpiration quantities for standard¬ 
ization periods are here considered as 1.00, while the corresponding ratio 
values for periods after spraying are expressed in terms of these. 
Tabi<S II. —Summary of the average data from Table /. Ratio values of A' to B for 
periods of ter spraying are relative to the ratio values of A to B for standardization periods 
expressed as 1.00 
Plant. 
Duration of 
experiment. 
Transpiration 
(ratio A':B). 
Ricinus communis . 
6 days. 
1. 5© 
2. 12 
2*39 
I- I 7 
I.63 
I. 8l 
3- 72 
43 
T-37 
Datura metaloides . , 
4 days 
Phaseolus vulgaris . 
10hours.... 
...do...... 
Beta cycla . 
Raphanus sativus . 
...do . 
Calodium sp. 
...do. 
Hibiscus cardinalis . 
...do.. . 
Clerodendron balfouri . 
...do.. . 
Datura metaloides . 
11 hours. .. 
Average. 
1. 99 
66848°—16——3 
