(Edema of ihe Tomato. 109 



Transpiration is less active during the night than in the day, not 

 only because of the lower temperature of the air, but especially because 

 of the absence of light,* During the winter season when plants are 

 grown in the forcing houses the nights are much longer than the days 

 and the total amount of transpiration in 24 hours, other things being 

 equal, would be less than what wonld take place in the open during the 

 summer months when the days are much longer than the nights. Add 

 to this the marked number of cloudy days during the winter, with a 

 low sun offering at best but a feeble light, and the conditions for tran- 

 spiration are still more unfavorable. 



Still another factor must be considered which deprives the plants of 

 much light, the structure of the forcing house itself. The light is not 

 so intense when it passes through glass, though the amount of light 

 thus cut off may be very little. However, the frame work, walls and 

 partitions do cut off an appreciable amount of light. 



These considerations, showing a lessened amount of transpiration 

 compared with what takes place under .natural conditions when the 

 plants are grown out doors, would place root pressure in excess of tran- 

 spiration should the conditions for root pressure under both circum- 

 stances be the same. 



With the comparatively small amount of light carbon assimilation is 

 lessened, so that the plant under the forced conditions of growth, when 

 it needs larger quantities of carbohydrates has to do with really a less 

 quantity than is supplied in the open where conditions for rapid growth 

 are not so favorable and those for assimilation are improved. 



Soil temperature compared loith that of the air. Some observations 

 made upon the temperature of the soil and air in the tomato house 

 indicate that the soil is maintained at a temperature only a few degrees 

 below that of the air. A sufficient number of observations have not 

 been made to show what bearing the difference in temperature between 



*Sach's Physiology. 



Good ale, Physiological Botany. 



Unger, Seitzungsb, Wien, Akad, Bd. xliv, 2, 1861. 



Deherain, Compt. Rend. Paris. T. Ixix. 



Masure, Ann. Aronomique, T. vi, fasc, pp. 441-500. 



Reinitzer, Sitzungsb, d. K. K. Acad. Wiss., 1881, I. 



Leclerc, Ann. Sci. Nat. Bot. T. xvi, 1883, pp. 231-379. 



Kohl, Die Transpiration der Pflanzen, Braunschweig, 1886. 



Eberdt, Die Transp. d. Pfl. u. ihre Abhang. v. aus Bed. Marburg, 1889. 



Burgenstein, Material zu einer Monographie der Transpiration, Verhand- 

 lungen d. K. K. Zool Bot. Gesellsch, Zu Wein Vol. 37, 1887, pp. 691-782, and 

 Vol. 89. 1889. 



