488 BOTANICAL GAZETTE [juxe 



end of the 12 or i6 day period recorded. The following results 



were secured: f 



Gram kcn per cubic foot of air space 



o.ooi 



0.002, temporary depressive effects 



0.003 



0.004, intermediate effects 



0.005 



0.006, temporar>' stimulative effects 



0.007 



0.008, relatively permanent depressive effects 



o . 009 



o.oi 



It is interesting to note that the greenhouse white fly (Aleyroides) 

 was killed at a concentration of 0.006 gm. KCN. Another point 

 worthy of emphasis is that the actual difference in amount between 

 a concentration of cyanide which brings about noticeable injury 

 to the plants, and one which does no harm, may be very small 

 indeed. This compares very well with previous statements (3, 9) 

 that cyanide either killed or that recovery was complete. 



There is not much work which can be cited in substantiation 

 of the mixed stimulative and depressive effects found. In the work 

 with hydrogen peroxide (4) very low concentrations of cyanide 

 accelerated the reaction. Again it was discovered (7) that cyanide 

 hastened the oxidation of an amino acid when the amino acid was 

 present in an impure state. With these two exceptions the cyanide 

 hterature bearing on this work deals with inhibitory actions. 



Factors 



EXTERNAL FACTORS 



Moisture.— In considering moisture as an external factor we 

 deal only with the effect of free water on the leaf surface of the 

 plants fumigated. It is common knowledge among greenhouse 

 men that if plants go into the fumigation wet, considerable injury 

 is often induced. In testing this I have found that some species are 

 made more susceptible to injury by wetting the leaves, while other 

 species are not visibly affected. The tomato is in this latter class. 

 On closer observation it was found, in the case of the tomato, that 



