4i 4 Delf . — Transpiration in Succulent Plants . 
2. The Cactaceae transpire less than any plants examined, whether 
reckoned on equal surfaces or equal fresh weights. 
The work of both Stahl 1 and Rosenberg 2 points to the fact that many 
European halophytes possess the power to transpire freely, as judged by 
the cobalt paper test. I have shown , 3 and have often observed, that in 
many of our British salt-marsh plants the transpiration may be much 
greater for equal transpiring surfaces than in a typical mesophytic plant ; 
in others the value approaches, but rarely falls below, that of the typical 
mesophyte under similar conditions at the time of the experiment. The 
figures in Table II give some of these results ; but since the observations 
were made of necessity at different times , 4 the transpiration is estimated per 
hour per square decimetre, relative to the loss of a water surface measured 
at the same time under the same experimental conditions, the latter value 
per hour per square decimetre being taken as ico in each case ; the varia- 
tions in transpiration due to the purely physical effect of the environment 
are now eliminated, as Livingston 5 pointed out. Throughout the experi- 
ments the transpiration observed is that of detached leafy shoots with no 
water supply ; the cut end was sealed immediately after being severed from 
the plant, and the fresh weight at once obtained ; the shoot was then 
allowed to transpire, hung up in the air of the laboratory, away from any 
draught or direct sunlight, and the water loss during the first hour or two 
hours of withering determined by means of an accurate balance. The values 
obtained will be somewhat below those of the normal plant, since, in all the 
plants examined, the stomata close within the first half-hour of experiment, 
and also because the transpiration falls off as the water content of the whole 
plant falls below the normal. 
Table II. 
Relative Transpiration per hour per sq. dm . 
Water ioo 
Salsola Kali 64-1 
Mesembryanthemum edule 66-9, 47*6 
A triplex portulacoides . . 61-7 
Salicornia 32 
Sedum spurium .... 36*0 
,, Sieboldii .... 49-6 
Saponaria officinalis . . 27*6, 7*4 
Vicia Faba .... 26-0 
Aster Tripolium ... 22*4 
1 Stahl, E. : Einige Versuche iiber Transpiration und Assimilation. Bot. Zeit., 1894. 
2 Rosenberg, O. : Uber die Transpiration der Halophyten. Ofvers. af Kongl. Vetenskaps- 
Akad. Forhandlingar, Stockholm, 1897. 
3 Delf, E. M. : Transpiration and Behaviour of Stomata in Halophytes. Annals of Botany, xxv. 
4 These figures are taken mostly from unpublished experiments made during the months of 
August and September, 1911. 
5 Livingston, B. E. ? The Relation of Desert Plants to Soil Moisture and Evaporation. 
