4 



BULLETIN 907, U. S. DEPARTMENT OF AGRICULTURE. 



that the effect is observable to the naked eye. Burned signifies 

 severe injury amounting to the partial or total discoloration of 

 numerous leaves, as by heat. Singed indicates slight burning, espe- 

 cially at the tips or edges of leaves. 



Varying degrees of damage to the plants were indicated as follows 

 in all experiments: 



— Plants entirely unaffected externally. 



1 — Some of the tenderest undeveloped leaves or tips of tender 



shoots at least slightly injured. 

 2 — Tenderest tips with undeveloped leaves severely injured; fully 

 grown tender leaves sometimes slightly affected; mature 

 leaves uninjured. 

 3 — Tender growth, including fully developed new leaves, destroyed; 



old leaves slightly affected. 

 4 — Mature leaves in large numbers severely burned. 

 5 — One-half to entire plant severely burned. 



THE EFFECT ON PLANT INJURY OF TEMPERATURE, LIGHT, AND MOIS- 

 TURE BEFORE FUMIGATION. 



The fumigation of growing plants is usually conducted without 

 regard to their environment prior to the gas exposure, barring the 

 factor moisture relative to which a divergence of opinion exists. The 

 experimental evidence presented hi this paper bearing on prefumiga- 

 tion conditions draws attention not only to the influence of moisture 

 but also to that of temperature and light. Data on the influence of 

 these factors are brought out in experiments 1 to 9, inclusive, as well 

 as in 11, 12, 14, 15, and 18, these latter experiments being discussed 

 under the subject of postfumigation influences. Certain of these 

 experiments, namely, 1, 2, 12, 14, 15, and 18, are of special value 

 by reason of the number of postfumigation environments also in- 

 cluded in each experiment. 



EXPERIMENT 1. 



Condition during fumigation, shade, 58°-60° F. 



Dosage, H ounces KCN. 



Date, March 18, 1915, 8.45-9.45 a. m. 



Plants in each test, 2; total, 30. 



Remarks: Plants somewhat hardened. 



Results. 



Condition after fumigation. 



Condition before fumigation. 



Dark, 

 60° F. 



Shade, 

 58° F. 



Sun, 

 68° F.i 



Dark, 60° F 



Shade, 58° F 



Dark, 86° F 



Shade, 90° F 



Sun, 72° F 



1 

 1 



2 + 



2 + 



3 + 



1 

 1 



2+ 



2 + 



3 + 



3 

 3 

 5 

 5 

 5 



1 Plants in sunshine for 2 or 3 hours before, fumigation. Maximum sun temperature for day, 77° F. 



