1095 
Relationships of the Gnetales. 
increase with the diameter of the stem. As Bailey 1 has shown this has had 
an important effect on the structure of the stem, for it has resulted in the 
production of the so-called depressed segments alternating with projecting 
ones. The depressed segments had formerly been considered to represent 
the ‘ interfascicular * wood. Fig. 30 shows the presence of the dip in 
E. calif or nica, and its increase in the successive annual rings. Owing 
to the lack of association between broad rays and leaves in Ephedra 
the depression has not the regularity which it exhibits in the oak. 
To summarize the important features of ray structure : The most 
primitive condition is obviously that presented by the first-formed secondary 
wood which has uniseriate rays, the individual cells of which are lignified. 
In both these respects, the uniseriate condition and the lignification, the 
rays differ from those of the Cycads and Bennettitales, and resemble those 
of the Conifers. For the rest the relationship is with the lower Dicoty- 
ledones, as is manifested by the process of compounding, the ultimate 
multiseriate condition, the presence of false rays, their retardation of the 
growth, the form and arrangement, and especially the pitting of the 
individual cells. A condition typically Dicotyledonous has therefore been 
derived from a condition typically Coniferous in a method which is to 
be expected from a study of Dicotyledonous anatomy. 
The different constituents of the secondary wood which we have been 
considering show very little specific variation, so that a diagnosis on the 
basis of wood structure would be very difficult to make. What variation 
exists is mainly one of degree. Thus E. monostachya has more septated 
wood parenchyma cells than the others ; E. Gerardiana and E. monostachya 
exhibit a greater tendency towards the ring-porous arrangement of the 
vessels ; E. calif ornica usually presents a larger number of ‘ false 5 rays, &c. 
But these features vary greatly in different pieces of wood and in different 
regions of the same plant. Accordingly, it is very difficult to make a 
specific diagnosis with any degree of certainty. But this difficulty is only 
in keeping with the recognized conservatism of vascular structures. 
Bast. 
The bast of Ephedra , unlike the wood, shows little indication of 
Angiospermous affinities. Indeed, except for the presence of broad rays, it 
is typically Gymnospermous. 
Fig. 34 represents a transverse section of the bast as well as the 
cambium and a little secondary wood. The biseriate ray in the centre 
of the field is seen to broaden out in a characteristic manner. In addition 
to the ray parenchyma there are other bast parenchyma cells which are 
arranged in radial rows and elongated vertically. They do not bear the 
1 loc. cit. 
