the Embryo and Seedling in the Gramineae . 181 
and axis the bundle is enclosed in an endodermis. The single group of 
xylem is composed of a few tracheides, often hardly lignified at all. They 
are commonly annular, but occasionally spiral. In the scutellum the xylem 
group is turned towards the ventral surface ; in the axis it is inverted—that 
is, directed away from the centre (Text-fig. 19, III and IV). The phloem is 
massive throughout, but appears single except just below the node, where 
the trace is prepared to branch to right and left as it enters the stele. 
The structure of the first node is obscured by the formation of 
a vascular girdle (PI. X, Fig. 9), on which the cauline roots are inserted 
(G in Diagram I, Text-fig. 19). The plumular traces lose their identity in this 
girdle, but some of them reappear just as the coleoptile traces P and P' are 
entering the stele (Diagram II, Text-fig. 19). One trace is opposite the 
gap which opens to receive P and P' } and must represent midrib M from 
the first leaf. 
Above the cylindrical base of the coleoptile is a region where it shows 
in transverse section as a crescent on one side of the stem-bud. Here the 
two bundles are symmetrically placed as regards the outline of the crescent, 
but not at either end of a diameter of the axis as in Avena . They both lie 
on the same side of this diameter ; that side which is opposite to the midrib 
of the first leaf. At this level the xylem of each bundle consists of a few 
narrow elements but little lignified. In transverse section the outline of the 
phloem is almost kidney-shaped, but there is no definite division into two 
groups. This structure is continued downwards, and—when the coleoptile 
traces enter the axis—preparations can be found in which the central 
xylem strand is seen to be bordered on either side by phloem elements 
(Diagram II, Text-fig. 19). 
The coleoptile traces P and P' approach the stele in opposite directions. 
They commonly travel along the same straight line, which is approximately 
tangential to the circumference of the stele at the point where a gap has 
appeared in the root-girdle (Diagram II, Text-fig. 19). Each has already 
split into two branches, one running outwards, and the other keeping 
nearly to the original line of approach (PI. IX, Figs. 7 and 8). In the 
three younger seedlings examined, the inner branch of P on its way to the 
gap is seen to unite with the lateral plumular trace adjacent to it, and 
the inner branch of P' carries off the corresponding trace on the other side 
of the stele. These junctions are masked in the two older seedlings by the 
insertion of numerous cauline roots. The inner branches unite to form 
trace x t which fills up the gap in the stele. The outward branches form 
the inverted scutellum trace sc. (Diagrams II and III, Text-fig. 19 ; PI. IX, 
Figs. 7 and 8). 
The reader will naturally conclude from the above description that the 
node of Zizania resembles that of Avena , except that its structure is less 
clear, and that this lack of clearness is due partly to the reduction of 
