421 
some Species of Gleichenia. 
side of them. The outline of the xylem is not disturbed by the upper pro- 
toxylem-groups, hence there are no promontories on the upper surface of 
the xylem-ring. 
Node, &c. 
In the present instance the lowest cross-section affected by the node 
was at a distance of 2-9 cm. behind the axil of the petiole, or 2 -6 cm. 
behind the point of complete separation of the leaf-trace from the stele. 
The first stage of preparation for nodal structure had been reached in the 
section shown in Plate XXIX, Fig. 3 ; here the protoxylem-elements at y 1 
have become slightly scattered, and the parenchyma in their neighbourhood 
has increased in bulk, forming the beginning of a nodal island. In sections 
cut serially towards the growing apex it was next noticed that, towards the 
inner side of this mass of parenchyma, a few elements of protophloem, and 
subsequently metaphloem, arose ; meantime the protoxylem branched, and 
formed two clusters, one at each end of the parenchymatous island. In the 
middle of the latter a few fibres were soon discernible ; the lowest section 
containing them showed one fibre only, surrounded by an endodermis ; but 
even this did not appear until the phloem had increased to about twenty 
elements, all of which were situated on the inner side of the group of scleren- 
chyma, and were separated from the endodermis by a single layer of 
parenchyma. By this time there was a radial band (Plate XXIX, Fig. 3, 
r. b.), composed of about three layers of xylem-parenchyma, connecting the 
parenchyma of the island with the inner mesocycle. This band of paren- 
chyma next became broader, and the phloem spread into it from either end, 
until the phloem of the nodal island and the inner phloem of the solenostele 
were eventually united. At this stage a few elements of protophloem 
(Plate XXIX, Fig. 4, ab.pk.) were noticed in the nodal island on the abaxial 
side of the sclerenchyma. These elements were nowhere connected with 
the rest of the phloem, but they persisted for about 4 mm. along the rhizome, 
and then disappeared. The effect of the failure of this phloem on the 
petiolar bundle will be discussed later. 
Groups of fibres now arise near the protoxylems y% and 73, and even- 
tually near j/ 4 ; they increase in size, and, one by one, become joined to the 
original nodal mass of sclerenchyma belonging to yi, the parenchyma 
becoming united first in each case. Protophloem-elements also arise inde- 
pendently near each of the lesser sclerenchyma-groups, and afterwards unite 
to form a continuous band of phloem in the composite nodal island, on the 
inner side of the sclerenchyma. As the radial band (PI. XXIX, Fig. 5) 
broadens, the sclerenchyma at the centre of the stele, and that of the nodal 
island spread into it, so that the two masses become united by a narrow 
strip having phloem on each side of it. The cross-section of the scleren- 
chyma is now T-shaped (cf. Boodle, ’ 01 , PL XXXIX, Fig. 26). Each of 
