1878. ] The Beneficial Influence of Plants. a. 
viously published experiments!; and, in order to establish this 
rate an extract from the summary of these investigations will be 
_ introduced, since they were instituted with the object of estab- 
lishing the rate of transpiration: 
In clear weather the evaporation by night, as compared to that 
which takes place in the day, appears to be about in the ratio of 
one to five. In some cases no loss occurred on dewy or cae 
indoors. Under eae yet bison cvaporanie at night was 
about the same indoors as in the open 
The rate of transpiration during the ‘ay showed a very differ- 
ent relation, giving a ratio of two to one in favor of the open air. 
Of the whole amount evaporated during twelve hours, in the day 
experiments, half was given off between the hours of II A. M. 
and 3 P. M., as shown > repeated testin 
the plant, and amount transpired. e mean eo and 
average dew point have also been recorded in the table 
i 7 
No.| Name of Plant. | BxPeriment| Evaporation. P Surface. © Weight of Plant. femp dew pe 
I UNE aes haat 12 hours | 2850 grains | All parts green 2 lbs, 2 oz. bs oi bes 
2° Ptaerininm 266s = 3500 eS Se Me ei nae 44201 grains | Sie 
3} Dre os ae n 1975 i 450 square in’s | 192 64.5° | 49.69 
4 | Hydrangea. .. 2. r 2858 he 744 +: 2170 73 | 56.7 
PUET U E ak i 710 t 479 e E fas ene 75-5 | 63.3 
G + Dantene 3 ie ors Me gie *S 330 i 720 grains | 75.1 | 61.7 
et Diten.. oe oe 2422 ind 817 velar Bas serie ae 75.5 | 62 
After an inspection of this table, the average rate of evaporation 
for soft thin-leaved plants, in clear weather, may be put down at 
about one and a quarter ounces per day (twelve hours) for every 
square foot of surface. The Lantana shows nearly two ounces 
to the square foot of surface. The camellia, with its dense smooth 
leaves, api e less than half an ounce to the square foot of 
surface, per : 
* * A few calculations may serve to impress 
de EE of the ratio of transpiration deduced from these 
weathe 
Car an ng the calculation further, a grove consisting of five 
hundred trees, each with a leaf surface equal to that of the elm 
mentioned, would return to the atmosphere 3906 tons of aqueous 
! Compare this with journal for March, 1878, p. 160. 
