Relationships of the Gnetales . 
1097 
Root. 
The root of Ephedra presents few features of special interest. The 
primary wood is diarch and small in amount. In the large primary root 
near the base of the stem it is arranged in two triangular masses whose 
outermost apices are occupied by the two protoxylem groups, and whose 
broad bases are separated by a lignified pith. In the secondary roots the 
primary wood is very small in amount and extremely difficult to recognize. 
Indeed, in most cases it appears to have completely disappeared, as has the 
fundamental parenchyma, so that the centre of the root is occupied by 
a solid mass of secondary wood. 
This secondary wood is in all essentials like that of the stem, differing 
chiefly in the relative amounts of the various constituents. Thus the wood 
parenchyma is more abundant and the rays larger, features which are to be 
anticipated from the function of the root in storage. The vessels are also 
more frequently of the primitive type, and the bars of Sanio more con- 
spicuous. 
Leaf. 
The leaves of Ephedra occur in opposite decussating pairs or in whorls 
of three according to the species. They are extremely reduced, in most 
cases being small brown functionless scales a few millimetres in length. In 
seedlings and young plants they may be much better developed, probably 
reverting to an ancestral condition. They then consist of a sheathing base 
and long needle-shaped extremity. 
A section through the sheathing base of one of the best developed 
leaves is represented in Fig. 38. Only the thickest part of the leaf in the 
region of the vascular bundles is included. Laterally, where it joins its 
fellow of the opposite side the leaf is only two or three cells in thickness. 
Stomata are exceedingly rare, but when present are deeply sunken like 
those of the stem. The mesophyll is not differentiated into layers and 
contains at best very little chlorophyll. 
Such a leaf as this is enormously developed in comparison with the 
ordinary adult leaves, which are only three or four cells thick. Moreover, 
the cells soon become thick- walled and perish. In most cases sclerenchy- 
matous fibres are scattered throughout the substance and may occasionally 
be arranged in bundles as in the stem. 
The tissue of the leaf is early separated from that of the stem by 
the development of a layer of absciss periderm. The whole of the sheath- 
ing base is involved. In Fig. 42 the dark band across the centre represents 
the periderm layer, below which is the tissue of the cortex and leaf-trace, 
and above is the empty thick-walled mesophyll of the leaf. The presence of 
the absciss periderm is a distinctly Angiospermous character. 
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