Nov. 12,1917 
Greenhouse Fumigation with Hydrocyanic Acid 
325 
meanwhile being kept in the dark. At the close of the fumigation one 
norm#! and one fumigated plant were selected for respiration meas¬ 
urements, the others being returned to the greenhouse to observe the 
extent of injury. The pots and soil surface of the two experimental 
plants were thoroughly paraffined to avoid the evolution of carbon dioxid. 
The plants were put into their respective jars, the latter sealed tight with 
paraffin, and the air freed from carbon dioxid. For the first day or two 
the respired carbon dioxid was measured every three to six hours, as is 
shown in figure 6. Since the atmosphere in the jars quickly became sat¬ 
urated with moisture, transpiration nearly ceased; hence the plants were 
not under normal conditions in this respect, and as a result there was a 
general decline in respiratory activity during the first 30 hours. As both 
a/ooaps AfA-r&r /w/Gstr/av 
Fig. 6 .—Curves showing the rate of respiration (in milligrams of carbon dioxid per hour per i gm. of dry 
matter in plant) of four pairs of tomato plants. From top to bottom the groups are arranged in order of 
increasing injury from hydrocyanic-acid fumigation. 
plants, however, were under the same conditions throughout, it was not 
deemed necessary to install a drying medium in the jars. At the end of 
the experiment the plants were removed and the dry weight of each de¬ 
termined, to form a basis for calculation. Although in all four of the 
experiments carried out the fumigation dose was the same, there was. 
considerable difference in the gross effect on the plants, owing to other 
varying factors (15). The first showed no apparent injury; in the second 
the leaves curled, but did not wilt; in the last two the smaller leaves 
and stems wilted, and some did not recover. This selective injury pro¬ 
duced different types of respiration curves. 
As is shown in the two upper curves, a slight injury results in a material 
decrease in the amount of respired carbon dioxid at the end of the fumi¬ 
gation. This is followed by a rapid recovery not only to normal, but in 
