96 GREENHOUSE Fl' M 1( ;.\!l( i \ 



th(>u,qh the azalia in thickness ahnost ecfualed tlie citrus, the stain- 

 inii' with safranin gaAC a very faint pink in azalia compared with 

 the deep pink or red of the citrus. 



The concentration of hydrocyanic acid i^as to wliich these lea\es 

 were exi)Osed was much higher than wouhl l)e encountered in 

 fumig-ation. but the results are comparable. Hydrocyanic acid gas 

 can enter plants through their cuticle but to a lesser extent or not 

 at all in the case of thick, strongly ctitinized cuticle. (General obser- 

 yations show that the fumigation, in the dark, of plants with closed 

 stomata. will injure those with thin cuticles, such as lettuce, toma- 

 toes and cucum])ers. far more severely than those with thick, strong- 

 ly cutinized cuticles, such as citrus, aspidistra, etc. The following 

 experiment will serAe as an example. The dose was 10 ozs. of 

 potassium cyanide per 1.000 cu. ft. for one and a half hours. Of the 

 plants present the lettuce, tomato and cucumber Avere completely 

 destroyed, half of the leaves of the transdescantia Avere btirned, 

 the youngest leaves of the geranium and crimson rambler, and the 

 growing ti])s of the wy and A'inca were injured while the azalia. 

 aspidistra, citrus and nasturtium were tminjtired. 



From the evidence cited, the conclusion may l)e drawn that 

 hydrocyanic acid enters the plants during ftmiigation through the 

 stomata if they are open and also through the cuticle, depending 

 upon its thickness and degree of cutinization. The question can 

 now be considered as to the role of moisture and temperature on 

 the ])enetration of the gas. 



MOISTURE. 

 Influence of Moisture Present In the Greenhouse. 



Inasnmch as hvdrocA'anic acid is soltil)le to infinit}' in water 

 any moisture present in the greenhouse at the time of ftmiigation 

 must be important. All the water present in the greenhouse on 

 the walks, on the glass, in the soil, on the plants, or in the air dis- 

 solves the hydrocyanic acid liberated by the charge. Penny (5) 

 has shown that in a closed room about 509^ of the hydrocyanic 

 acid is lost within ttne hour after the beginning- of the fumigation, 

 while wet leaves will account for 23% in hve minutes and wet soil 

 3H^/r in a similar period. 



]\Ioisture ])resent in the greenhouse during fumigation there- 

 fore tends to reduce the quantity (tf hydrocxanic acid present in 

 the air. 



