Barber.— The Structure of P achy thee a. II. 147 
One of the most remarkable circumstances connected with 
these slides is the varying manner in which the structure is 
preserved. It is not easy, by the examination of any one 
slide, to make much progress ; but, by the careful comparison 
of a selected series of specimens, certain of the difficulties, 
which have hitherto clustered around the study of this plant, 
may be removed. 
For the sake of clearness I shall refer to the slides selected 
for description under the numbers 1-13. The figures con- 
tained in my former paper 1 I shall refer to as B 1-14, and 
those in Sir Joseph Hooker’s paper 2 as H 1-12. 
DESCRIPTION OF SECTIONS. 
It is a fortunate matter that Mr. Storrie has succeeded in 
cutting no less than four sections in different planes through 
a single specimen of Pachytheca. As these slides may throw 
light upon the question of the oval bodies , I shall deal with 
them first. 
Slide 1 (Figs. 1 and 1 a) contains a radial section through 
one half of the spherical body of the plant. The medullary 
portion is, to a great extent, absent, being represented by a 
few small fragments close to the zone of oval bodies. The 
cortex is well shown, and consists of a series of radiating 
tubes, sometimes branching, of clear light yellow substance, 
bordered by well-defined thick walls. These tubes are 
separated from one another by elongated spaces, usually 
rather wider than the tubes, terminating towards the medulla 
in slightly broader rounded ends. The spaces are bridged 
across by crystals of the light yellow substance, but are not 
filled by it : the remainder of the spaces being unoccupied, 
or more or less filled with a darker, brown, granular mass. 
It will thus be seen that it is perfectly easy to distinguish 
the clear radiating tubes from the broken spaces between 
them ; and it is equally easy, by comparison with the figures 
1 Annals of Botany, III. 141. 
2 Ibid. III. 135. 
