154 
CONTRIBUTIONS TO BOTANY. 
tem. I have noticed, however, that the wood of Ephedra is 
regularly zoned, as in other exogenous plants ; for a trans- 
verse section of a branch of Ephedra Andina which I possess 
shows five distinct concentric rings, the intervals between the 
medullary rays exhibiting numerous longitudinal hollow air- 
cells. The branches of Gnetum, on becoming dry, separate 
readily at the nodes by distinct articulations ; but such separa- 
tion rarely takes place in Ephedra. On the other hand, a lon- 
gitudinal section of a new branch of the latter genus shows that 
the central pith of one internode is not continuous with the pith 
of the next internode, nor with that of their accessoiy branchlets; 
for the ligneous fibres of the several internodes which enclose the 
pith, and which constitute the wood, all converge to form a 
sort of plexus or solid diaphragm across each node, much after 
the manner of the stem of a Bambusa. 
This pith is quite homogeneous, consisting of oblong, square, 
parallel cells (hexagonal in their transverse section), with very 
thin transparent walls, which are pitted with few, minute, opake 
dots. The wood is hard, formed of fine, simple, indurated 
fibrous tissue, closely compacted ; these longitudinal fibres, under 
a powerful microscope, appear marked by dark glands lying 
aci’oss them at irregular distances, which are either transversely 
linear or oblong, thus giving them almost a scalariform appear- 
ance, the walls themselves being pitted with minute and almost 
invisible specks ; these are crossed by very numerous transverse 
medullary rays of similar structure, which extend from the pith 
to the bark. In the first two or three rows of the longitudinal 
fibres or ducts next the pith, the markings are so very close 
that they have much the appearance of uncoilable tracheae; but 
I have nowhere been able to find any true spiral vessels. Inter- 
spersed among the. longitudinal woody fibres, are the many hol- 
low air-tubes before mentioned, of three or four times their dia- 
meter, which appear uninterrupted throughout the entire length 
of the internode : their walls are extremely thin and translucent ; 
and it is upon these only that we find the large circular spots 
(apparently fenestrations), which are well shown in Lindley^s 
‘ Introduction,^ pi. 2. fig. 7. It will hence be seen that there is 
no analogy between this structure and that of the Coniferce, 
where the annular disks, which so conspicuously mark the Gym- 
nospermous families, are always found upon the ligneous fibres 
themselves, and not upon the air-passages, as in Ephedra. The 
structure is equally different from that of the young branchlets 
of Casuarina, where the pith crosses the nodes and is continuous 
throughout the branches. 
There is a peculiarity in the bark of Ephedra that may be 
worth recording : it is filled with strong ligneous fibres, as in 
