70 EXrEKLMENT STATION. [Jan. 



nald, Mr. W. V. Tower and Dr. C. II. Hooker ^ in the entomo- 

 logical greenhouse. Thej found that sunlight, cloudy weather, 

 moonlight, drops of water remaining on the foliage and too high 

 a moisture content of the atmosphere were all conducive to burn- 

 ing, and that less burning occurred on cloudy nights or clear 

 nights without moonlight. The best results were obtained by 

 fumigating on clear, starlight nights, with little or no moon- 

 light, or on dry, cloudy nights with a tem2)erature range of 55° 

 to 65° F. 



Some observations recently made by Mr. S. S. Grossman in 

 our liiborntory show among other things that the stomata or 

 breathing pores, as always believed, close quite rapidly when 

 subjected to darkness, and open in the sunlight, and that vari- 

 ous gases result in a closing of the stomata. Mr. Grossman did 

 not have an opportunity to finish his work, but Mr. G. H. Chap- 

 man, research assistant, intends to continue it the coming year. 

 If the burning of leaves is caused by gases entering the stomata, 

 and if the stomata are closed by gases, then it is not apparent 

 why foliage should burn more severely in the daytime than 

 at night. Some experiments made a few years ago in our lab- 

 oratory by Mr. 11. M. Jennison, on the effects of various gases 

 on transpiration, showed that when-plants are subjected to gases 

 transpiration decreases rapidly, but in most of these experi- 

 ments, as well as in some of our own with illuminating gas, 

 there occurs a secondary rise in the transpiration curve shortly 

 after the first drop. From these experiments it would apjiear 

 that various gases cause a marked retardation in transpiration 

 at first, followed by a brief but marked acceleration, after which 

 a general retardation in transpiration follows. ^ It is possible 

 that the stomata of the gas-treated plants may open again 

 shortly after being closed by the gas, and finally close again. 

 Observations on this point, however, are not sufficient for us to 

 draw any definite conclusions. 



The effect of burning on foliage is varied, in some cases 

 merely the margin of the leaves being burned. Sometimes 

 burning takes the form of numerous small spots on the leaf, 



» Twenty-first Ann. Rept., Mass. Agr. Exp. Station. 1909, p. 73; Twenty-second Ann. Rept., 

 Mass. Agr. Exp. Station, 1910, p. 214. 



« .Iiimelle found fs-c Sfihneider, Bot. Gaz,, Vol. XVIII,. p. 57) that sulfuric ether increased 

 transpiration in lieht and retarded it in darkness, while Schneider found that by this treatnnent 

 transpiration was retarded under all conditions. 



