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The Plant World. 



same after being corked in twelve hours with 0.5 cc. 

 of illuminating gas. This Shows that 0.5 cc. of illuminating 

 gas per 20,000 (1 part in 40,000) causes the complete closing of 

 the flower in twelve hours or less. Higher concentration caused 

 a more rapid closing and a marked inrolling of the petals. Even 

 0.2 cc. per 20,000 causes considerable closing in twelve hours, 

 though not as marked as 0.5 cc. 



The effect of duration of exposure was also tested. No 

 injury was done to a bud just ready to open upon one day's 

 exposure to 2 cc. of gas per 20,000 (four times killing concen- 

 tration for three days' exposure). On a similar bud 5 cc. for 

 one day was considerably more injurious than 0.5 cc. for three 

 days. The stigmas 'did not project, but the petals were markedly 

 discolored. During the entire period of experimentation there 

 was no very marked variation in the toxicity of the gas used. 



The experiments with ethylene were begun by exposing 

 buds just begining to show the petals to 1, 1-2, 1-4, 1-8, and 1-16 

 cc. of ethylene in 20 liters. In each of these concentrations the 

 buds were killed on three days' exposure. The usual signs of 

 gas poisoning were noted; petals turned yellow and withered, 

 and the stigmas projected. Since it was evident that these 

 concentrations were far above the toxic limit, we resorted to the 

 use of a 2 per cent, mixture of ethylene with air. Various 

 amounts of this were used, until the toxic limits were definitely 

 located. With 2 cc. of this 2 per cent. mixture in 20,000 (1 part 

 in 500,000), the results were similar to that obtained with 1 cc. 

 of gas per 20,000 (1 part in 20,000). In Fig. 2a is a bud, just 

 showing the petals, exposed to this concentration of ethylene for 

 three days. Also 1 cc. of 2 per cent, ethylene per 20,000 (1 part 

 in 1,000,000) gives results similar to that shown by 0.5 

 cc. of illuminating gas per 20,000 (1 part in 40,000). 

 The growth of the petals is not sufficiently retarded to make 

 the stigmas conspicuous; the petals remain fresh for 

 several days but never open farther. Where much 



less than 1 cc. of 2 per cent, ethylene per 20,000 was used 

 with similar buds, three days' exposure did not prevent their 

 opening. 



