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Stomata in Halophytes . 
and are therefore much easier of observation. Plants examined from the 
Cambridge Botanic Gardens in July, 1909, and others growing in an arti- 
ficial salt marsh in Dulwich, in September, 1910, possessed stomata, the 
guard cells of which moved with ease and rapidity. This is contrary to 
the result of Stahl, 1 who found that in his cultivated halophytes the stomata 
were open, but immovable. 
In the artificial salt marsh at Dulwich there was but one plant of 
Aster tripolium. This had been grown for some months successfully, 
and had been watered at intervals with a 2 % solution of common salt. 
At 8 a.m. on September 20, just before the sun was on this part of the 
marsh, a strip of epidermis was removed from both sides of one of the 
leaves, mounted dry and examined on the spot under a microscope. 
The stomata were widely open in each case, but they half closed whilst 
still under observation in less than three minutes. At this time the relative 
humidity in the neighbourhood of the plant was found to be 93-5 %. The 
whole plant was now darkened for an hour by being covered with dense 
black cloth. A strip of epidermis from one of these darkened leaves 
showed about half the stomata with the pore narrowly open, whilst the 
remainder had the pore completely closed as far as could be seen in surface 
view. The relative humidity of the air around the plant during the time 
of darkening was 93*1 %, and this change is so slight as to have a negligible 
effect on the stomata. 
The plant was then uncovered and was exposed to the sunlight, which 
now fell directly on the leaves. After an hour of such illumination half the 
stomata on a strip of epidermis were still closed, and the remainder had 
the pore about half-way open ; the relative humidity had, however, fallen 
to 78 %, and very shortly after all the leaves stood less erect and began to 
appear limp and flaccid. 
Some fine plants of Aster tripolium were received in November, 1910. 
These had many large and healthy leaves, all of which showed only closed 
stomata. Exposure to sunlight, bright diffuse light, and to electric light, 
either in dry air or nearly saturated air, did not cause these stomata to 
open, and this may have been due to the temperature or, more probably, 
to the time of year. 
From the foregoing observations it may be concluded that the stomata 
of Salicornia and of Aster tripolium (two of the most typical British halo- 
phytes) do not show the features characteristic of either a xerophilous plant, 
as Schimper’s theory would lead one to expect, or of a freshwater marsh 
plant as Stahl supposed. They rather resemble those of a typical meso- 
phyte in being superficially placed, capable of opening and closing, and 
sensitive to light and to changes in the humidity of the atmosphere. 
From preliminary observations it may be added that the stomata of 
1 Stahl, E. (’94> : Einige Versuche iiber Transpiration und Assimilation. Bot. Zeit., 1894 . 
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