TEACHERS DEPARTMENT. 
33 
ago it appears that the traveler Burchell picked up on stony ground 
an object he mistook for a pebble, but which on examination 
proved to be a plant of the genus Mesembryanthemum. Both in 
color and in form this plant, previously named M. truncatum, pre¬ 
sented a remarkable resemblance to the stones among which it 
grew. A second species, M. bolusi , growing on the hills around 
the Karru, generally produces two leaves about the size of a 
duck’s egg, which have a surface like weathered stone, and a 
brownish gray color tinged with green. In this state it closely 
resembles the surrounding stone, although for a short time its 
bright yellow flowers render it conspicuous enough. M. nobile 
is very similar. A fourth species of the same genus, together 
with Anacampseros papyracea (in which the leaves are covered 
with white papery stipules) resembles the quartz pebbles among 
which it grows. In the author’s opinion M. bolusi, M. nobile, 
and perhaps M. truncatum (which, unlike some of the other plants 
mentioned, do not change their characters under cultivation) may 
afford instances of true mimicry.”f 
A curious and apparently quite useless physiological behavior 
of the scission layer in the sweet-gum ( Liquidambar styraciUua) 
is worth drawing attention to. In other trees and sometimes in 
this one, the activity of the scission layer terminates when its 
function is completed, that is, then, with leaf fall. In the tree 
which I have in mind the growth of this layer continues during 
the succeeding seasons in such a manner that a curved column of 
cork is formed of the length of a half centimeter or more. At 
the top of the column, which is directed distally, the original leaf- 
scar can be seen, and some trace of the influence of the vascular 
tissues may be detected in the cork on sectioning. The cork 
columns remain discrete for two or three years usually after which 
they may be more or less disguised by the cork wings (character¬ 
istic of this plant) which are formed and which, by anastomosis, 
finally quite hide the original condition. F. E. L. 
The so-called unifoliate species of Streptocarpus are un¬ 
usual in their morphology. According to Fritsch,* who confirms 
f Nature, 71: 232. 5 Jan., 1905. 
* Die Keimpflanzen der Gesneriaceen. Jena, 1904. 
