By 
22 Absorption of Water by the Leaves of Plants. [J anuary, 
of pressure on the absorption were next examined. A chestnut 
branch dipped in water was found to transpire hourly sixteen — 
grammes per square metre; when inserted into a tube of water and 
subjected to the pressure of a column of water twoand a-half metres 
high, the evaporation amounted to fifty-five grammes per square 
metre per hour, and the branch, at the end of five hours, weighed 
more than at the commencement. As to the effect of the epi- 
dermis in restraining evaporation, he found that an apple deprived 
of its skin loses fifty-five times as much water in the same time 
as one with its skin entire ; while similar experiments in the case 
of a cactus leaf showed a difference in the proportion of fifteen 
to one. Losses by rapid evaporation lessen appreciably the phy- 
siological energy of leaves. Thus an oleander leaf containing 
sixty per cent. of water, when introduced into an atmosphere 
containing carbonic acid gas, decomposed sixteen c. cm. ofthe 
gas; one containing thirty-six per cent. of water decomposed 
eleven c. cm.; while one containing twenty-nine per cent. of water — 
was without action. As respects the relative power of evapora- — 
tion possessed by the upper and under surfaces of leaves, he found | 
the average proportien in a dozen different kinds to be as one in — 
the former to 4.3 in the latter case. 
Boussingault then proceeded to investigate the question of the — 
ability of leaves to replace the roots of a plant in serving as the © 
agent of absorption. A forked branch of lilac was so placed that — 
one portion was immersed in water in a reversed position, while — 
the other was exposed to the atmosphere, the superficies of foliage — 
in both portions being the same. The transpiration from the — 
exposed portion was found to be the same as under normal cir- 
cumstances, and after the lapse of two weeks the foliage was as , 
fresh as at the commencement, showing that the submerged leaves 
were fully able to replace the roots in supplying the shoot with — 
moisture. A vine-shoot half plunged in water maintained a nor- | 
_ mal evaporation in the free foliage, and remained fresh for over a _ 
month. An oleander shoot, under similar circumstances main- a 
tained its normal appearance for four months. With the arti- 
= choke it was found necessary that the amount of surface of leaves _ 
beneath the water should be four times that above it. A number _ 
of experiments, with regard to the power of leaves to absorb — 
water in the state of vapor from a saturated atmosphere, showed _ 
we ee could do this only when they had previously lost a por- 
Pye eee 
er ance Weak as oa 
