I9I9] 



CLA YTON—FUMIGA TION 



487 



somewhat detrimental to the growth of the plant. With o . 004, 

 stimulation and retardation effects seem to be about balanced ; but 

 at 0.005, 3.nd continuing up through 0.006 and 0.007, stimulation 

 eiTects plainly dominate. The plants giving these responses 

 retained after the treatment all appearances of normal growth and 

 metabolism. 



With the concentration of 0.008 gm. KCN the first injury 

 appeared, although there was some variation in this regard. Thus 

 in one series no injury appeared before o.oigm. KCN. The 

 harmful effect of this injury was very marked. Growth records 

 were taken for concentrations up to 0.016, but unfortunately, with 

 these damaging strengths (0.008-0.016), growth records do not 

 always indicate the true condition of the plants. False stimulation 



TABLE III 

 Percentage increase or decrease in growth following fumigation 



KCN per cubic foot 



Percentage 



I St to 4th 



day 



Percentage 



5th to 8th 



day 



Percentage 



gth to 12th 



day 



Percentage 



13th to i6th 



day 



0.007 gm.: no injury 



o 008 gm.: injury to parts of 



plants 



o 009 gm. : injury to all plants 



o.oi gm 



0.012 gm 



+ 14 



+36 

 -37 

 -27 

 -16 



+32 



+44 

 + 2 

 -29 

 -40 



-33 



-58 

 -63 

 -66 

 — 12 



-16 



-44 

 -58 



was frequently shown. This is an increase in growth rate of plants 

 ob\dously in poor condition. The explanation of this false stimula- 

 tion is that the growing tips of plants are rarely killed, and in con- 

 sequence of the loss of considerable leaf area through injury these 

 growing tips are forced into renewed activity. Thus badly injured 

 plants in the course of a month's time form entire new tops, 

 although old injured leaves drop off, for the most part. Usually, 

 however, when injury occurred the depressing effects were so strong 

 that this increased growth rate was very transient in character, or 

 did not show at ail, as is seen in table III. 



A characteristic feature of this injury is the duration of the 

 depressive effects. The plants were still far below normal at the 



