493 
Stomata in Halophytes . 
The Mercurialis and * apple green ’ Salicornia were started practically 
simultaneously ; both have the power of closing their stomata on wilting, 1 
but in Salicornia , notwithstanding this, there is seen a considerable rise in 
the cuticular transpiration during the early afternoon ; and this probably 
only fell off when increased sap concentration acted as an inhibiting factor, 
diminishing the possible water loss. Suaeda and ‘ crimson red * Salicornia 
were started under the atmospheric conditions which caused the increase in 
transpiration in Salicornia , and they show only a steady decrease during the 
afternoon hours. 
. Further experiments at Erquy, both on growing and on detached shoots, 
led to the conclusion that under ordinary conditions transpiration in the 
halophytes mentioned is of considerable magnitude ; that in dry air it would 
be greater than the supply of water from the roots would allow ; and that in 
nature this is to a large extent obviated by the fact that the layers of air 
next to the damp earth of a salt marsh contain much more water vapour 
than the higher layers, whilst periodic flooding renders a large amount ol 
absorption of water possible over the whole surface of the plant ; but this 
point will be considered more fully subsequently. 
In July, 1909, with the permission of Professor Seward, further experi- 
ments were made at the Cambridge Botanical Laboratory. Some healthy 
and smooth-stemmed plants of Salicornia annua were very kindly sent by 
Professor Oliver from Cley ; these were green, and no forms approaching the 
J crimson red ’ type were available. The experiments were made in the dry 
air of the laboratory (humidity 60 %), but more precautions were used 
than had been possible in the field laboratory at Erquy ; an accurate 
chemical balance was used throughout. 
On July 23 the transpiration of a detached shoot of Salicornia annua 
was compared with that of leaves of Sedum spurium and Vida cracca. The 
former was the most suitable succulent xerophyte and the latter the most 
convenient mesophyte at hand. 
A healthy shoot of Salicornia was measured, detached, and the cut end 
sealed with wax mixture of low melting-point, and a small loop of cotton 
was fixed to this end. It was then suspended in nearly saturated air under 
a bell-glass, while two leaves of both Sedum and Vicia were treated 
similarly. When all were hung up in the saturated air, they were weighed 
in order and the time noted ; they were subsequently weighed at intervals 
of 20 minutes, during which time they had been suspended in bright diffuse 
light in the ordinary still air of the laboratory. 
The following table shows the loss of water in these leaves at intervals 
of 20 minutes during the first three hours of exposure. Throughout this 
period the temperature varied from 19-8° C. to 20-8° C., and the humidity from 
55% to 57%, chiefly owing to intermittent clouds: between 12.50 p.m. 
1 Cp. Rosenberg (’97), See also later experiments. 
