1913.] PUBLIC DOCUMENT — No. 31. 63 



The normal plants were grown in the same bench but were 

 not screened, and the light conditions were the same as those in 

 the greenhouse. The house is new and the light excellent, — 

 only about 18 per cent, less than out of doors. The relative 

 light intensity under the various conditions varied sufficiently to 

 cause considerable difference in the development of the plants. 

 These differences were determined by chemical methods accu- 

 rate enough to warrant the average relative light conditions 

 being obtained, but not adapted to measure the absolute light 

 intensity. 



In the following tables are given the results of experiments 

 with the effects of different light intensities on the growth of 

 cucumber plants and their susceptibility to burning from hy- 

 drocyanic acid gas. In each experiment 6 groups of plants 

 were used, i^o. 5 being grown under normal greenhouse condi- 

 tions and the others under varying light intensities. 



Since two of the screened compartments gave practically the 

 same light intensities, and the results obtained from the j^lants 

 in these sections were similar, they were averaged together and 

 appear in the table under I^o. 2. The plants were grown in 

 7-inch pots and entirely under the screens. The moisture content 

 of the soil was kept fairly uniform in each series. After the 

 plants had reached a certain degree of development they were 

 placed in a tight glass case containing about 30 cubic feet, and 

 each series was fumigated at the same time under similar 

 conditions as regards exposure and the amount of hydrocyanic 

 acid gas. The plants were all fumigated with .007 grams of 

 cyanide per cubic foot, a strength commonly used in greenhouse 

 work, and known as formula ^ 1-2-3, — one part cyanide, two 

 parts sulfuric acid and three parts water. After imdergoing 

 this treatment for forty minutes to one hour the plants were 

 removed from the case and the results noted. 



1 Bui. 123, Masa. Agr, Exp. Station, 1903. 



