the Embryo and Seedling in the Gramineae. 
199 
Comparison of the Zea type with the A vena type. 
In these two types the scutellum is inserted at some distance below the 
first node. The region of the main axis which separates them has been 
called the mesocotyl. 
In the Arena type the scutellum trace on entering the axis turns 
sharply upwards in the cortex and does not join the stele until it has 
reached the first node. In fact, the trace behaves like the main bundle of 
a separate stalk running upwards from sucker to node. It is easy to con¬ 
struct stages of development in which such a stalk might become united 
with the main axis. Arena would then represent the epoch when external 
union was accomplished, but the vascular systems of the two members were 
still distinct. 
In the Zea type the process of fusion has gone further. The scutellum 
trace runs upwards within the stele, but can still be distinguished from the 
other constituents with more or less certainty. 
C. Triticum type. 
The third anatomical type of Grass seedling distinguished by Van 
Tieghem possesses no mesocotyl. The apparent insertion of the scutellum 
takes place at the first node. We have now to examine the relation of this 
type to the others, assuming that some such relation can be established. 
Triticum rulgare, Vill. The external features of the seedling are 
shown in Text-figs. 25-7, p. 200. The leaf within the coleoptile becomes the 
first foliage leaf. Two cauline roots are formed very early, and soon equal 
the primary root in length. 
The scutellum is rounded at the apex. It contains slender vascular 
bundles, which collect lower down into a single bundle-trunk. The epithe¬ 
lium is confined to its dorsal surface, merely tipping the apex and fringing 
the ventral wings. The bundles either terminate under these fringed 
margins, or in the neighbourhood of the dorsal epithelium. At a level 
rather nearer the insertion than the apex, a main trunk is formed by union 
of all the upper bundles. They approach along lines converging from both 
margins and from the dorsal surface ; their bases in transverse section look 
rather like the sticks of a fan. 
The main bundle-trunk when first formed is much extended laterally. 
Its xylem is a thin ventral plate, bisected by a few protoxylem elements. 
Its phloem is shaped in transverse section like a flat plano-convex lens. 
Just below the apparent insertion of the scutellum, however, the bundle 
becomes more compact. 
The real insertion of the scutellum on the axis can be followed with 
accuracy in those seedlings only where the plumule lies in a straight line 
with the primary root, and is fairly parallel to the midrib of the scutellum. 
