the Embryo and Seedling in the Grammeae . 185 
Two other plumular strands are perceived in the stele for the first time 
as the coleoptile traces enter it. They represent Z 3 and L\. Trace P 
makes its way between Z 2 and Z 3 , and trace F between L\ and Z' 3 , just 
as in Avena. Even the xylem arch is present, though far less massive. 
The large xylem vessels of the lateral plates make their appearance to 
right and left of M during the formation of the mesocotylar stele. At 
first they are numerous and poorly lignified. Lower down, where the stele 
has assumed its final form, each lateral plate consists of three or four large 
lignified elements. 
The structure of the first node in Lolinm italicum is very clear because 
the nodal roots are mere rudiments without vascular tissue at an age when 
the stele of the mesocotyl is fully defined, and some of the plumular traces 
are lignified. The lower cauline root-system is also tardy in development, 
and the transition from mesocotyl to primary root can therefore be followed 
better in the stele of Lolium than in that of Avena or Zizania. The 
details, however, are not very clear. In one seedling—the younger of the 
two—the xylem breaks up into four crescents, convex towards the centre. 
Protoxylem elements are found at their extremities, and the result is 
a pentarch root-stele. In the older seedling there are at first three xylem 
groups, not definitely crescent-shaped. Here, too, the stele of the primary 
root becomes pentarch. 
B. Zea type. 
Sorghum vulgare , Pers. The seedling structure of this species is 
clearer than that of Zea, because the formation of cauline roots is delayed 
until the appearance of the second leaf, both at the first or plumular node, 
and at the insertion level. We have therefore chosen this species for 
detailed description, and it will represent the type named from the better- 
known genus Zea. 
The seedling drawn in Text-fig. 20 A, p. 186, has just reached the age 
when the first leaf is about to push through the slit near the tip of the 
coleoptile. This still sheathes the stem-bud, and is borne on a fairly long 
mesocotyl. The primary root is long and unbranched. There are as yet no 
cauline roots. 
We have examined the vascular skeleton of five seedlings, including 
that mentioned above, Two of the others are younger, and two older. 
The oldest shows two foliage leaves, but no cauline roots are visible ex¬ 
ternally. The vascular structure in all five seedlings is singularly uniform. 
The scutellum has a single bundle with massive phloem, but com¬ 
paratively little lignified xylem. In the upper part, branches are given off 
freely towards the dorsal surface of the scutellum, which is covered by 
an active epithelium. In this region the xylem elements are scattered 
about the periphery of the main bundle, but even here they are far more 
