4 i7 
Delf. — Transpiration in Succulent Plants, 
It was established by Czech, 1 and has been confirmed by Volkens and 
other observers, that, in general, the stomata of plants growing in wet or 
even damp situations are more numerous per unit area than are those of 
dry places. Thus Veronica Chamaedrys was found to have 175 stomata 
per sq. mm., whilst Veronica Beccabunga had 248. So far as I have been 
able to observe, this holds true also for succulent plants, those from dry 
regions, such as some species of Mesembryanthemum and Sedum } having 
considerably fewer than have those, such as Salicornia , from marshy places. 
Table III gives the distribution of the stomata of such plants as I have 
observed, and also a few of Czech’s figures for comparison. 
According to Burgerstein 2 the degree of opening of the stomata afifects 
the amount of transpiration far more than the actual number present. 
Leitgeb 3 was the first to call attention to the power of the stomata to open 
and close, and regarded it as a means for regulating the amount of trans- 
piration. This view has been widely accepted, but has been objected to re- 
cently by Lloyd, 4 who found that in Fonquiera splendens and in Verbena ciliata 
the £ rate of transpiration may undergo sudden and wide changes, without 
the accompaniment of a sufficient change in the dimensions of the stomata 
to account for them on the theory of stomatal regulation of transpiration.’ 6 
According to Lloyd the capacity for diffusion of the stomata of Fonquiera 
is well in excess of what would be required for the greatest observed trans- 
piration rate, and he therefore concludes ‘ stomatal regulation of transpira- 
tion does not occur, though of course conservation of the contained water 
follows on complete closure of the stomata. It is open to doubt, however, if 
this condition ever obtains.’ On the other hand, some experiments of Dr. F. 
Darwin, a preliminary account of which was given at the meeting of the 
British Association, 1910, and a further account of which is now in the 
press, lead to the conclusion that in many plants, if they can be observed by 
a sufficiently delicate method, stomatal movements are found to correspond 
closely with changes in the rate of transpiration caused by alteration in 
external conditions. It is clear, therefore, that the whole question of 
stomatal regulation requires further investigation. 
So far as the power of movement of the guard cells in the stomata of 
succulent plants is concerned, we have but little direct evidence. In 
xerophytic succulents the stomata may be so much sunken or overlaid by 
cuticle that they seem to have little or no scope for movement. Stahl, 6 
however, states that the stomata of xerophytes all possess the power 
to close, and they are, therefore, presumably capable of the reverse action. 
1 Burgerstein : Die Transpiration der Pflanzen, p. 210. 
2 Burgerstein: ibid., p. 21 1. 
3 Leitgeb : Beitrage zur Physiologie der Spaltoffnungsapparate, 1886. 
4 Lloyd, F. E. : The Physiology of Stomata. 
6 Lloyd, F. E. : ibid., p. 137. 
6 Stahl : Einige Versuche iiber Transpiration und Assimilation, 1894. 
