204 Sctrgant and Arber .— The Comparative Morphology of 
These changes in structure are more readily compared with those 
recorded in Triticuni and Arena when they are described in the inverse 
order, that is, from above downwards. 
Seven traces from the first leaf and two bundles from the coleoptile 
enter the first node from above. This does not include the midrib trace m 
from the second leaf, which is commonly present at the beginning of the 
first node. But as it splits into two branches which unite with two lateral 
traces from the first leaf before the first node ends, it is not considered as 
having a course distinct from theirs. Some traces—usually unlignified 
at this age—which represent the lateral bundles of the second leaf, also 
enter the first node; and in the older seedlings examined, certain strands 
on either side of m can be traced back to the bud in the axil of the coleo¬ 
ptile. Sooner or later all these traces are absorbed in the root-plates 
(I and II, Text-fig. 29). 
The midrib trace M from the first leaf remains distinct throughout the 
node, and is always opposite the gap left by the defection of m. Lower 
down this gap is filled by the temporary union of the two coleoptile traces 
P and P '; and a branch from each trace turns downwards into the stele 
while they are still in contact. Their phloem groups are distinct at first, 
but soon form a crescent external to the common xylem group, which 
contains, besides the two xylem branches from the coleoptile traces, some 
central elements from the scutellum bundles (III, Text-fig. 29). 
Thus, at the base of the first node, we find within the stele a single 
bundle M facing a compound bundle ;r, built up of branches from P and 
P\ together with xylem elements from the scutellum traces. These bundles 
M and x are separated from each other on either side by a plate of xylem 
and phloem (r/, rp'), derived from the lateral traces of the first and second 
leaves (IV in Text-fig. 29). This very definite structure is completely 
obliterated a little lower down by the insertion of four cauline roots, and 
when the confusion introduced by them has disappeared, the main stele of 
the axis is found to be root-like. 
This accounts for the internal branch from each coleoptile trace. But 
the larger portion of each trace pursues its course through the cortex of the 
axis, and enters the scutellum. Turning sharply upwards, each coleoptile 
segment becomes one of the two bundle-trunks described above (^ 15 sc 2 , II 
and III, Text-fig. 29). 
The Hordeum seedling differs from that of Triticum chiefly in two 
points: in the presence of two scutellum bundles, and in the absence of any 
approach to a mesocotyl. We might have attributed the second character 
to the youth of the Hordeitm seedlings examined, but by the kindness of 
Mrs. Taylor we have been able to compare our series with another cut by 
her from an older specimen. This corresponds in age with the older 
