324 
Journal of Agricultural Research 
Vol. XI, No. 7 
The data in figure 5 show that with catalase, as well as with the oxi¬ 
dases, there is a temporary decrease activity at the close of fumigation, 
followed by a rapid recovery. The catalase differs from the oxidase 
activity, however, in that it not only recovers to the normal but that it 
actually exceeds the normal in considerable degree. The increase above 
normal at the end of the series of samples is much more marked than the 
decrease below normal at the beginning, which is the reverse of that 
found in the oxidase curves. 
Reductase.—R eductase activity could not be demonstrated in tomato 
leaves by the methylene-blue method of Shafer (19). 
« 
EFFECT ON RESPIRATION IN TOMATOES 
Certain effects of hydrocyanic acid upon some of the individual enzyms 
connected with respiration in plants having been demonstrated, it was 
next deemed advisable to study the effects of the gas on the respiratory 
process itself. 
Fig. 5.—Curves showing the effect of hydrocyanic-acid fumigation on the activity of the catalase in tomato. 
A and B, juice used; C and £>, leaf powder used. 
The amount of carbon dioxid given off by a plant in the dark during a 
specified period was used as the index of comparative respiration between 
fumigated and unfumigated plants. The respiration chamber was a glass 
jar 30 cm. high and 13 cm. in diameter, fitted with a ground-glass stopper, 
through which were drilled two holes, one for intake and one for outlet of 
air. A black bag impervious to light inclosed the jar. The carbon 
dioxid was absorbed in a Truog tower of beads containing standard 
barium hydroxid (21). Another tower of beads containing saturated 
barium hydroxid was used to free the ingoing air of carbon dioxid. In 
order to avoid laboratory air, a long tube connected the apparatus with 
the outdoor air through a window. By means of a water pump air was 
aspirated vigorously through the apparatus for 40 minutes. It was 
found by testing against pure calcite that this length of time for this sized 
chamber always gave 95 to 98 per cent recovery of the contained carbon 
dioxid, which was sufficiently accurate for the comparative purposes at 
hand. Two jars and two plants, one normal and the other fumigated, 
were always run side by side, and all conditions were as nearly identical 
as possible. The temperature varied from 20° to 25 0 C. Five or six 
potted tomato plants from 15 to 20 cm. high were put in the dark for 
an hour. Three of them were then fumigated in the dark, the others 
