354 Takeda . — Some Points in the Anatomy of 
nor annular vessels have been observed. The xylem-parenchyma is 
exceedingly scanty. There are no sclerenchymatous fibres present. 
The structure of the vascular bundles of the cotyledon (Fig. 9) and of 
the young leaf hardly differs in essential points from that of the adult leaf. 
The xylem consists of annular and spiral tracheides of protoxylem, and of 
dense spiral and reticulate tracheides with scattered bordered pits. A few 
unlignified fibres occur on the phloem side (Fig. 9, set. /.). In the mature 
part of the young leaf these fibres also occur on the xylem side. 
The * Transfusion-tissue \ This tissue is remarkably well developed 
in the leaf of Welwitschia, and has been described and figured by Hooker 
( 7 , p. 19, PI. IV), de Bary ( 4 , pp. 335, 383, Fig. 157), Bertrand ( 1 , p. 16, 
PI. II, Fig. 1), and Sykes ( 19 , p. 182, PI. XVII). I have here very little to 
add to de Bary's accurate and detailed description ( 4 , p. 382). This tissue, 
which surrounds both the main bundles and veins, forms an almost complete 
sheath of tracheides of usually one or occasionally two layers. This tracheidal 
sheath is, in the case of the main bundle, usually separated from the vascular 
elements by either a layer of parenchyma on the side, or by a mass of 
sclerenchyma on the upper and lower side of the bundle. The cells lateral 
to the bundle are much narrower than the other ; they are elongated and 
have reticulate thickening, while those above and below the bundle are 
much larger, nearly isodiametric, and have reticulate thickening or small 
bordered pits between meshes of the thickened bars (Fig. 7, w. t.). The 
degree of bonification of the cell-wall is, so far as the reaction of phloro- 
glucin shows, less than in the xylem elements of the bundle, as Zimmermann 
( 23 , p. 7) observed in certain Conifers. 
In my material of the three-week-old cotyledon and of the six-month- 
old leaf I have noticed some elements of the ‘ transfusion-tissue * have made 
their appearance on the lateral side of the larger bundles. Particularly 
towards the apex of the young leaf the ‘ transfusion-tracheides * are fairly 
abundant (cf. 19 , p. 183). They are usually separated from the bundle by 
a layer of parenchymatous cells, or occasionally join the xylem. Sykes 
states ( 19 , p. 214) that the first-formed elements arise on the phloem side 
of the bundle, but this is not the case with my material. The shape of the 
first-formed elements is more or less elongated in the direction parallel to 
the bundle. The membrane is lignified and possesses reticulate bars (Fig. 8, 
also cf. Fig. 9). 
I have dealt with the significance of this tissue in general in a special 
paper (21). 
The Mucilage Canal. In the adult leaf one often notices the presence of 
mucilage canals. These occur between bundles, and always on the phloem 
side. They are round in transverse section and comparatively short, varying 
from a few millimetres to as much as 1 cm. or more, and they run parallel 
