69 
SUNSHINE AND TRANSPIRATION (DEHERAIN AND MARIE- 
DAVY). 
Studies in the transpiration of plants were made in England as 
early as 1691 by S. H. Woodward, who experimented on aquatic 
plants. He showed that the consumption of water by the plant, or the 
welght of water evaporated from it, varied within narrow hmits, 
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 
6 grains of the rich water of the Thames was required to make the 
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 
these 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. 
a  —  — I Ii i i 000 ii 
I Weight of 
pes 
Plant. Exposure. Tempe ue per hour 
| per gram 
weight of 
leaf. 
2.6% Gram. 
Wiheatiese== sea so52 SUNSHING Mal ees aon Sh on cs soos Pac ae eae eee sae ee 28 0. 882 
1D Yoys> = psn et aes Diffuse digit yee 2 sete ee De ea ae he oe coe cate 22 aia 
DOs eee ceeees Darknegs AG. 8 Seb sao ean ome 5 ea Naot ate 22 .O11 
Barley, sik 2 2 SUNSHINE ee eee oe ee oe Ge ge ee eas ohalees 19 . 742 
Doses: to Diffusedight 22-2 --- 22-2. - pasate Bo ae Se eS eee ees 16 . 180 
ID@345t eee DarkNESss ase gre ict ee oe eR ee te oS Lae cane cooe 16 023 
Wihestss- 0.2: Peel SUNSHINO 6 eee eee a See eee ce oe lay tes SSL 22 718 
1D Yo)S ues aoe se Dankn Oss esses 2 soos ae eee eee ee ee nee So Anes 16 . 028 
1X0) ee, ee ee SUMSHINGS sete ee eet ee Sees eee ee ker Nee Pe 28 . 703 
Wows hes ase = te Diffusedichtes-) sa2 45. —55 52 See SSRs ae fe eS 22 . 060 
Dose se Sse: BD) TENG SS Sees ede nes te a te en SE tee 22 007 
The effect of sunshine in stimulating transpiration is very clearly 
seen by a study of these figures. The small transpiration 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. 
