Experiments on Absorption of Salt-Marsh Plants. 123 
approximately to that of a *12 gm.-mol. salt solution are able to 
absorb water by osmosis, it seems probable that salt-marsh plants 
with their high osmotic pressures should be able to obtain water, 
not only from atmospheric moisture, 1 but also from the sea. 
In order to ascertain whether this is the case or not, experi¬ 
ments have been carried on at intervals during the summers of the 
last few years. Some few experiments were made at the Bouche 
d’ Erquy itself, but the majority were carried out in the Botanical 
Laboratory of University College, London, on plants brought from 
Erquy and other localities. The plants were always brought to 
London in sods with a considerable amount of soil, so that they 
should continue as much as possible under natural conditions. In 
all the experiments, small plants, for the most part unbranched, 
were chosen, and great care was taken to use only those with 
the epidermis uninjured. 
Absorption of water by the assimilating surface of a plant can 
be proved to have taken place if an actual increase in the weight of 
the plant is found after immersion ; if there is an increase in the 
percentage of water in the tissues after immersion, or if, in the 
case of absorption from a salt solution, there is an increase in the 
strength of the solution after plants have been immersed in it. 
In dealing with the question of absorption in Saliconiia, most 
of the work was done with a view to finding out if there was an 
increase in the weight of individual plants after immersion. Some 
experiments were also made to find out the effect of immersion on 
the water-content of the plants, and an attempt was made to 
ascertain the effect of immersion of plants on the strength of a 
sodium chloride solution. 
Methods of Estimating the Absorption of Water 
by Aerial Parts of Plants. 
(i.) By Estimating the Differences in the Water-Content of 
Immersed and Unimmersed Plants. 
Plants, as nearly as possible alike, were chosen from the same 
place, the succulent parts of some were weighed, immediately dried 
at 100"C and weighed again. The succulent parts of others were 
> By atmospheric moisture is meant vapour from a very damp 
atmosphere as well as precipitated moisture, such as rain, 
dew and mist. 
