On the Occurrence of Lens-cells in the Epidermis 
of Mesembryanthemum pseudotruncatellum. 
BY 
F. SUMMERS, M.Sc. 
Hartley Botanical Laboratories , University of Liverpool. 
With ten Figures in the Text; 
OME of the means of protection against excessive insolation, possessed 
by certain species of Mesembryanthemum belonging to the section 
Sphaeroidea, have already been drawn attention to by R. Marloth ( 7 ). 
Among the species described by this author were M. opticum , Marloth, 
M. truncatellum , Haworth, and M. Hookeri , Berger. Further, Marloth has 
instanced a case of so-called mimicry on the part of M. calcareum , Marloth, 
the aerial portion of which bears a striking resemblance to the limestone 
pebbles and fragments of the Karroo (8). 
For M. truncatum , Thiselton-Dyer pointed out that the plant has not 
only assumed the spheroidal form and the accompanying minimal transpiring 
, surface, but, in order to escape the attentions of animals, it has imitated the 
form of a water-worn pebble (11). 
To the aerial portion of M. opticum , Marloth has applied the descriptive 
term ‘ corpusculum which applies also to the other two species mentioned 
above. 
Each ‘ corpusculum * is from spheroidal to conical in form, and is com¬ 
posed of two similarly shaped leaves which in outward appearance in no 
wise resemble these organs. They are thick and fleshy, and grow together 
as far as their upper surfaces, where they are separated by a slit of greater 
or lesser extent. In the middle arise the two leaves of the next year’s 
shoot. Through the growth of this young leaf-pair the two older leaves 
are forced apart. They decline with the vegetative season, finally remaining 
as wrinkled withered sheaths clothing the base of the succeeding corpuscu¬ 
lum (Figs, i and 2). The upper surface of a corpusculum is more or less 
convex, and varies in appearance with the different species. It may be 
smooth, furrowed, wrinkled, or warty; or, as in the case of M. truncatum , 
figured by Thiselton-Dyer ( 11 ), it may possess a marbled and mottled 
appearance. 
[Annals of Botany, Vol. XXV. No. C. October, 1911.3 
