1096 Thompson . — The Anatomy and 
relationship of companion cells to the sieve-tubes, but are arranged rather 
in groups. 
The sieve-tubes themselves are visible in this photograph as smaller 
cells which lack contents and are somewhat collapsed. They are never 
present in abundance, but, as shown here, are usually confined to small 
patches. In very large stems of the American species which have been 
examined they become proportionately much more numerous. In longitu- 
dinal section they are found to lack well-defined end walls, but to be long 
and tapering, as is typical of Gymnospermous sieve-tubes. This feature is 
shown in the tangential section photographed in Fig. 35. The sieve areas 
are not confined to the end walls of the tubes, but are scattered rather 
uniformly along the lateral radial walls, as may also be distinguished in 
Fig. 35. The same condition is shown in radial section in Fig. 36, in which 
the sieve areas appear in face view. 
Outside the zone of actively functioning bast many of the cells collapse, 
but others become strongly sclerified. The latter are scattered singly or in 
small groups. They represent part of the parenchyma of the living bast. 
The bast of Ephedra , then, in all the characters of its sieve-tubes and 
in most of those of its parenchyma, possesses no Angiospermous affinities, but 
is typically Gymnospermous. Strasburger 1 states that in its general 
appearance and arrangement it resembles most closely the bast of Arau- 
caria. 
Cortex, Epidermis, etc. 
As may be seen in the transverse section of the entire young branch 
(PI. XCIV, Fig. 1) the external surface is strongly ribbed. Each rib marks 
the position of a bundle of sclerenchymatous fibres immediately below the 
epidermis (Fig. 1 and PL XCVII, Fig. 37). The fibres are extremely hard, 
and do not take the usual lignin stains. Others of the same type are scattered 
either singly or in groups through the rest of the cortex, and large groups 
occur in contact with the primary phloem. The outermost living cells are 
arranged more or less in the form of a palisade and are abundantly supplied 
with chloroplastids. Beneath this layer the tissue is more irregular and 
contains air-spaces. Thus the structure of the cortex is remarkably like 
that of a leaf, whose function it performs. 
The epidermis is thick-walled and heavily cutinized. It is abundantly 
supplied with stomata like a leaf, but these are confined to the furrows 
between the projecting ridges (Fig. 37). The guard cells are strongly 
lignified, and deeply sunken under overarching accessory cells (Fig. 37). 
The periderm formation which eventually throws off the cortex begins 
just outside the soft bast and inside the primary bast fibres. Its radial 
rows of cells are in line with those of the bast. 
1 loc. cit. 
