1 1 1 6 Michell. — On the Comparative Anatomy of the 
Clustered crystals of calcium oxalate are found in great abundance. In 
the large water-storing cells beneath the periderm, clusters occur which may 
extend over two or three cells. These clusters are larger, but otherwise 
resemble the second type described in the leaf (PI. XCVIII, Fig. 7). 
Clusters of the first type are abundant in the parenchyma of the stem. 
No starch is found in this species, probably owing to the fact that the 
material was obtained during the early part of the vegetative season. 
Throughout the stem, drops of some fixed oil occur. These stain 
easily with either a 1 per cent, solution of osmic acid or an alcoholic 
solution of alkannin, but of the two alkannin is the more reliable stain. 
Certain organic compounds, as well as oil, are stained black with osmic 
acid ; and as the mucilage ring stains easily with this acid, some organic 
compound must accompany the mucilage, which of itself is not affected by 
this reagent. The suberized cell-walls of the bark appear to be impregnated 
with some fat or oil, which, however, differs from the oil occurring in drops 
in being insoluble in ether, chloroform, or benzol. In the ‘ New Phytologist ’ 
an account is given by T. G. Hill of the use of c Scharlack R ’ as a micro- 
chemical test for oil in plant tissues. 1 Any oil present stains pink, while 
other substances are not affected. In Ceraria this reagent only stains the 
oil in the cell-walls of the bark, leaving the oil drops colourless. As these 
drops stain easily with both the other reagents used, the result obtained 
with * Scharlack R ’ cannot be considered a proof of their non-oily 
character. The cells of the innermost layers of the periderm have cellulose 
walls in which no oil is found. The oil appears simultaneously with the 
change in composition of the wall from cellulose to suber. 
C. namaquensis. 
The stem of C. namaquensis is very similar to that described above. 
The quantity of mucilage, however, is so great that sections cut and placed 
even in 70 per cent, alcohol swell immediately, and are unfit for staining. 
The chief differences are : 
(a) The bands of parenchyma separating the large water-storing cells 
are in this case extremely narrow. 
(b) Annual rings are absent, which fact, however, is not remarkable, as 
there are two rainy seasons a year in the regions in which this plant grows. 
(c) The material of this latter species was gathered at the end of the 
principal vegetative season, and therefore it is not surprising that large 
quantities of starch are found in the parenchyma throughout the stem. 
(d) The oil which is present in C. gariepina is found here as well, the 
only difference being that the quantity is considerably less. The suberized 
cells of the bark do not stain as deeply with alkannin in this species as they 
do in C. gariepina . 
1 Hill (’12), (10). 
