be go hin Bee 
1879. ] Absorption of Water by the Leaves of Plants. 23 
tion of their water of constitution, 2 e., that which is essential to 
their normal existence. Thus a wilted branch of periwinkle, 
weighing four grammes, after remaining for a day and a-half in 
an atmosphere saturated with aqueous vapor, weighed 4.2 grammes; 
after twelve hours immersion in water it weighed 9.4 grammes. 
His last experiments related to the power of leaves to absorb 
aqueous solutions. Drops of water containing 0.2 per cent. of 
calcium sulphate in solution were placed on the leaves of a great 
variety of plants under conditions favoring absorption, and pro- 
tected from evaporation by inverted watch glasses with greased 
edges. In most instances the drops were entirely absorbed, 
leaving no trace of the mineral matter. As in the case of pure 
water, the under surface of the leaf absorbed much more rapidly 
than the upper surface. Solutions of potassium sulphate and 
nitrate gave corresponding results; the absorption of solutions 
of sodium chloride and ammonium nitrate were not so perfect. 
It is obvious that these results must considerably modify the view 
at present held by physiological botanists, that the small quantity 
of ammonium carbonate contained in the air, which is believed to 
be the sole source of the nitrogen in the tissues and secretions of 
plants, can only be absorbed by the roots after having been 
brought down to the soil by rain. 
Mr. Henslow’s experiments, as detailed in a paper read at a 
recent meeting of the Linnzan Society of London, are altogether _ : 
in harmony with those of the French professor. The results of 
a very large number of experiments extending over several years, 
may be epitomized as follows : 
The absorption of water hy internodes. —The experiment con- 
sisted of wrapping up one or more internodes of herbaceous 
plants in saturated blotting-paper and in noting the effects. As 
a rule the leaves on the shoots rapidly perished, showing that 
transpiration was too great “for the supply. The stems, however, 
ii fresh for different periods up to six weeks. 
2. Absorption by leaves to see how far they could balance transpi- 
ration in others on the same shoot—The general result is that as 
long as the leaves remain green and fresh 3 in or on ig they act — 
as absorbents; but that the leaves in air keep fresh or wither 
according as the- ‘supply equals or falls short of the demand. _ 
3. To test how far leaves on a shoot can nourish lower ones on the 
same.—It appears that it is quite immaterial to plants whether _ 
they be supplied with water from the absorbing leaves being above _ 
or ce, those transpiring. Water flows in either direction mey oe 
wel DAN 
