igig] CLAVTON— FUMIGATION 485 



at any given time is extremely small ; while the proportion of active 

 potassium cyanide molecules is large. The number of active oxygen 

 atoms is also small. If we further assume that the cyanide unites 

 with the cystein at the same point where the oxygen ordinarily 

 combined, then the results obtained are easily understood." In 

 plant respiration, with cyanide present, we have the same general 

 condition; that is, the oxygen of the air is not able to oxidize the 

 plant compounds, and we may suppose that the cyanide has acted 

 in the same way. In the case of respiration, of course, we may have 

 a chain of several oxidations and reductions, and the exact point at 

 which the cyanide intervenes is not known. 



Material 



With the data at hand, while there is much on which to base 

 inferences, there is nothing which tells of the behavior of an auto- 

 troph and the factors influencing this. Consequently, since this 

 was pioneer work, it seemed highly desirable that it be done with 

 normal green plants under normal conditions. The tomato was 

 selected because it is easy to grow, sensitive to cyanide, and a plant 

 commonly requiring fumigation in the greenhouse. Work under 

 conditions such as those indicated is made difficult by the presence 

 of factors not under control, which vary conditions with the different 

 periods of time. In consequence of this it seemed best, in the case of 

 most of the material experimented upon, not to try to carry on the 

 work to its final expression, but merely to open up the way. The 

 writer hopes at a later date to complete the work upon some of 

 the more important phases with conditions carefully controlled. 



Responses 



The response of the plant to varying concentrations of hydro- 

 cyanic acid was observed as indicated by the subsequent growth of 

 the plant. Two main points were considered in deciding the effect 

 of a given concentration of gas: (i) the growth rate of the plants 

 after fumigation; (2) the appearance and growth character of the 

 plants after fumigation. The method was to select 7 or 8 groups 

 of plants, similar in all respects, and to fumigate these on successive 

 nights. Suitable checks were kept, and the growth of the treated 



