Vascular System of Matonia pectinata. 483 
to have increased considerably in diameter, and now possesses some fifty or 
sixty elements (Fig. 12). In its centre is a group of about half a dozen 
cells of rather smaller diameter than the tracheids and parenchyma sur- 
rounding them, possessing relatively thin walls which stain dark blue with 
haematoxylin, and no nuclei. This is the first appearance of unmistakable 
phloem. The cells in question are no doubt sieve-tubes. Associated with 
the sieve-tubes are an approximately equal number of parenchyma-cells, 
with nuclei which fill the greater part of the lumina, and dense granular proto- 
plasm ( prot . c ?). These are probably the 4 Eiweisszellen ’ of Strasburger, so 
widely distributed among Pteridophytes in association with sieve-tubes. The 
first two root-steles have no connexion with the strand of internal phloem. 
In the neighbourhood of the points of insertion of these steles, however, 
there are indications of the appearance of external phloem elements at 
various points on the periphery of the rhizome-stele, and these are con- 
nected with the phloem of the root-steles. Just in front of the second 
of these two roots the rhizome-stele stretches itself at right angles to its 
axis preparatory to giving off the second leaf-trace, and the internal strand 
of phloem follows the outline of the stele, and itself sends a contribution to 
the trace (Fig. 13, int . ph. tr.). The external phloem of the stele, which by 
this time has become a fairly well-defined layer, also contributes to the 
trace. The phloem of the leaf-bundle during its passage through the cortex 
appears to surround the xylem completely, though it is mainly massed on 
the adaxial side, and consists largely of parenchyma. A third root is 
inserted just behind and a fourth just in front of the origin of the second 
leaf-trace. Beyond this point the stele increases greatly in diameter, the 
central phloem-strand becoming particularly bulky. In the middle of 
the latter appear certain large, more or less isolated cells, which resemble 
the cells of the endodermis both in size and contents, and represent the first 
appearance of an internal endodermis. The stele becomes greatly elongated 
dorso-ventrally and three roots, which have not yet penetrated the cortex, 
arise from its ventral side. 
The tissue of the dorsal side of the stele now draws together to form 
the third leaf-trace (Fig. 14), which consists of an arc of xylem incom- 
pletely surrounded by phloem, that in the adaxial concavity of the arc 
derived from the internal phloem of the stele, while the sieve-tubes occurring 
on the lateral and abaxial faces of the trace are continuous with the external 
layer of the stelar phloem. The endodermis of the concavity of the trace 
is also continuous with the internal endodermal cells of the stem-stele. The 
external phloem of the stele beyond the point of departure of the trace is, 
of course, continuous with the adaxial phloem of the trace. We have here, 
in essentials, the relations of external and internal phloem of the stem-stele 
with leaf-bundle-phloem characteristic of the Linds ay a-type. \ 
1 Tansley and Lulham (’02). 
