SUNSHINE AND TRANSPIRATION (DEHERAIN AND MARIlS- 

 DAVY). 



Studies in the traiispinition of plants were made in Enjihind as 

 early as 1691 by S. IL Woodward, who oxiHM'iinonted on a(iuatic 

 plants. He showed that the consumption of water by the plant, or the 

 weight of water evaporated from it, varied within narrow limits, 

 while the growth of the plant under the same temperature and sun- 

 shine, varied according to the amount of nourishment in the water; 

 thus of pure spring water 170 grains had to be evaporated in order 

 to make an increase of 1 grain in the weight of the plant, but only 

 'M\ grains of the rich water of the Thames was required to make tlie 

 same increase in the weight of the plant. 



In 1848 Guettard, experimenting upon a creeping nightshade, 

 showed that a plant kept in a warm place without sunshine would 

 transpire less than one in a colder place with sunshine. 



Deherain, as quoted by Marie Davy (1880, p. 231) introduced the 

 leaves or stems of a living plant into a tube suitably closed; under 

 tliese circumstances, by reason of the small, calm space of air sur- 

 rounding the leaves, the evaporation in the ordinary sense would be 

 inappreciable, but the transpired water was found to increase the 

 weight of the tube, as shown in the accompanying table. 



Sunshine and transpiration. 



The effect of sunshine in stimulating transpiration is very clearly 

 seen by a study of these figures. The small trans])iration from the 

 leaf when kept in darkness is supposed to be, at least in part, due to 

 a persistency of the stimulus given to the plant by the light; so that, 

 as is well known, the growth of the plant goes on at its maximum rate 

 in the late afternoons, sometimes even after sunset, and does not 

 attain its minimum until early morning. 



