Ll. Lloyd 29 



in the dark 6 hours before dusk and then fumigated with a control plant 

 of similar nature; | oz. cyanide per 1000 eft., duration 9-|- hours, tem- 

 perature 61-5-53°, relative humidity 81 per cent. The plants kept in the 

 dark would presumably have had more opportunity to close the stomata 

 but were in no way protected against damage thereby as in each experi- 

 ment precisely similar burns developed on all the plants in each test. 

 The second experiment consisted in cutting with scissors the laminae 

 of the leaflets parallel to the chief lateral veins, and in cutting off the 

 tips of some of the leaflets. Four plants were treated in this way im- 

 mediately before fumigation so that the gas had free access to the raw 

 tissue. Although moderate burns developed no damage could be asso- 

 ciated with the cuts and the injury was much the same on cut and uncut 

 plants. After these experiments Prof. Blackman agreed that no simple 

 explanation of the mode of injury could be given and it is not proposed 

 to discuss it further. 



It was abundantly clear, however, that after daylight the most 

 important factor in fumigating with this gas was the turgidity of the 

 plant. An idea prevailed among the growers, and had found expression 

 in a tradesman's circular, that flaccid plants were very liable to damage. 

 For this reason flaccid and very turgid plants were repeatedly fumigated 

 side by side and in each case the foliage of the former escaped injury 

 while that of the latter was damaged (Plate II, figs. 4-7). On four 

 occasions series of five to eight large tomato plants in 1 2-inch pots were 

 prepared by withholding water from them on successive days till one 

 or two were flagging and one was excessively turgid while the remainder 

 were in intermediate conditions. On two occasions the test consisted 

 of the fumigation of two plants only, one flaccid and one turgid in each 

 instance. The fumigation greenhouse was heavily saturated with moisture, 

 except in one case, and the plants were then treated with | oz. cyanide 

 per 1000 eft., duration 9 hours. Flaccid plants and those approaching 

 flaccidity escaped any damage under the following conditions of tem- 

 perature and relative humidity: (1) 60-54°, 97 per cent.; (2) 66-5-61°, 

 88 per cent. ; (3) 67-59°, 67 per cent. ; (4) 69-60°, 97 per cent. ; (5) 58-55°, 

 90 per cent.; (6) 65-52°, 85 per cent. In each case turgid plants side 

 by side with the others were badly damaged, the injury being always 

 proportional to the turgidity. The two following experiments carried 

 out under still more adverse conditions illustrate the same point : 



(1) Two plants with four trusses set, one plant turgid and one flaccid, were 

 fumigated with the excessive dose of 1 oz. cyanide per 1000 eft., duration 9 hours, 

 temperature 04-59°, jelative humidity 86 per cent. The tui-gid plant had its foliage 



