4 - 1 8 Delf . — Transpiration in Succulent Plants. 
In a paper recently published by Linsbauer 1 on the physiological anatomy 
of the epidermis of some Bromeliaceae, it is shown that the stomata are 
surrounded by at least two pairs of subsidiary cells, which are arranged as 
though to protect the guard cells from contraction when the neighbouring 
aqueous tissue collapses. In the case of Quesnelia the stomata were found 
to be completely closed, owing to the formation of a membrane across the 
outer respiratory cavity. In many of the Bromeliaceae the arrangements 
of the stomata and of the air passages in the leaf seemed to be such as to 
ensure the best ventilation with the minimum of transpiration. 
In all the succulent plants which I have examined the stomata appear 
to be capable of movement, but I have frequently found the stomata of 
species of Sedum and of various fleshy halophytes in the closed condition, 
especially when the sun was on these plants and the weather dry. Stahl 2 
asserted, chiefly from the results of experiments made on the transpiration 
of halophytes grown in an artificial salt-marsh, that the stomata of these 
plants are not capable of closing. Stahl used the cobalt paper test, relying 
chiefly on the time of coloration of the dried paper ; but the careful observa- 
tions of Rosenberg , 3 using the same method and confirmed by means 
of direct microscopic examination, show conclusively that this is not the 
case, at least when the plants are growing in their natural habitat. Rosen- 
berg suggested that the inactivity of the stomata observed by Stahl was 
due to the culture conditions. However, in the artificial salt-marsh at 
Dulwich I have frequently observed that the stomata of halophytes possess 
the power of closing, and they appear to me to be especially sensitive 
to air of low humidity. The stomata of Salicornia annua and of Aster 
Tripolium also close in darkness . 4 
So far as I have seen, the stomata of succulent plants close during the 
earliest stages of withering, and this appears to me to be an adaptation to 
conserve the water supply as far as possible during time of need. Lloyd 5 
states that in Fouquiera splendens and in Verbena ciliata ‘ the beginning of 
closure occurs somewhat later than initial wilting, and seems to be a result 
of water loss by the leaf as a whole. There is no adaptive closure, meaning 
by this a closure in anticipation of wilting.’ On the other hand, Rosenberg 6 
found that when he observed the transpiration of the leaves of some halo- 
phytes (as A. triplex , Cakile maritima , Plantago maritirna ) immediately 
after detaching from the parent plant, a distinct drop in the rate of trans- 
1 Linsbauer : Zur physiologischen Anatomie der Epidermis und des Durchliiftungsgewebes der 
Bromeliaceae, 1911. Anz. Kais. Akad. Wiss. Wien, mathemat.-nat. Klasse, ix. 
2 Stahl, W. : Einige Versuche Uber Transpiration und Assimilation, 1894. 
3 Rosenberg, O. : Ueber die Transpiration der Halophyten. Ofvers. af Kongl, Vetenskaps-Akad 
Forhandlingar, Stockholm, 1897. 
4 Delf, E. M. : Transpiration and Behaviour of Stomata in Halophytes, 1911. 
5 Lloyd : The Physiology of Stomata, 1907. 
6 Rosenberg : Ueber die Transpiration der Halophyten, 1897. 
