222 Eames . — On the Origin of the 
by the complete absence of primary wood rays in the fibro-vascular 
segments. 
In Clematis the stem shows a definite number of bundles in the 
internode — twelve in C. virginiana , L., the species studied — alternately 
large and small. These lesser intermediate bundles are examples of 
those which are said by various writers to be laid down by the in- 
terfascicular cambium, and serve to fill the gaps between the original 
bundles, completing the solid cylinder. Lignification, indeed, appears first 
in the six large bundles (which are c common ’ bundles), forming proto- 
xylem. In the six smaller bundles the protoxylem is perhaps not formed 
within the internode proper, though in the node itself, and for a short 
distance above, it is well developed. Such a condition may be respon- 
sible for the view that the so-called ‘interfascicular bundles’ in general 
lack protoxylem. The cambial ring develops as before, appearing first 
in the bundles, and apparently only very slightly, if at all, sooner in 
the large than in the small ones, which can be seen outlined in the rapidly 
differentiating tissue. The interfascicular cambium is then formed, and 
increase in thickness proceeds as usual. No new bundles are formed, and 
only large rays occur. In comparison with Aristolochia we find the im- 
portant differences to be an almost complete localization of the proto- 
xylem in those large bundles from which the leaf-traces arise to pass 
out at the node directly above. 
These three plants, so commonly chosen to illustrate the fusion of 
bundles in the formation of a woody cylinder, present a good series for 
the demonstration of the opposite view. The arrangement of the proto- 
xylem in the stem of Quercus is very similar to that in the Gymnosperms, 
the larger leaf-traces, and ray changes influenced by them, causing the 
characteristic differences. The formation of large, originally compound, 
rays, setting off segments of the central cylinder, has been noted above 
as the cause of the misunderstanding of the course of development in this 
genus. In Aristolochia and Clematis we find the protoxylem more and 
more localized ; but, as stated above, these two plants belong to a class 
generally admitted to be highly specialized. There seems to be evidence, 
in the unquestionable suppression of the small rays, of a considerable 
evolutionary advance in the vines. Of the two genera at present under 
discussion the writer has been unable as yet to examine seedlings for ray 
development and location of protoxylem. The evolution of vines seems to 
have been along a line somewhat similar to that followed by the herbs. 
Use has been made by both of localization of protoxylem and of ray- 
parenchyma. The herb has also extended the transformation of xylem 
into parenchyma, and so has widened its interfascicular rays and reduced 
the size of its bundles. These changes remove the necessity for intra- 
fascicular wood rays, and they disappear gradually, becoming completely 
