Affinities of Per anema and Diacalpe . 249 
gap. The strands from any one leaf-trace are inserted on the lower half of 
the two limbs of vascular tissue enclosing the gap opposite the leaf, while 
the median main strand is inserted at the lower junction of these limbs 
(Fig. 4, I, 11). All the bundles from any one leaf-trace are inserted on the 
lower half of any leaf-gap. Evidently the upper half receives half the 
bundles from one leaf-trace which enters from a higher leaf and half the 
bundles from another. These two leaves are inserted on ,the axis obliquely 
above that of which the bundles enter on the lower half of the leaf-gap 
(Fig. 4, ill). 
This arrangement corresponds in the main with what occurs in the 
insertion of the leaf-trace on the dictyostele in Nephr odium filix-mas. But 
in the last-named Fern the adaxial bundles of the leaf-trace enter at the 
level of the bases of the gaps corresponding to the two leaves obliquely 
next above that to which the bundles belong. The median main strand 
enters at the fork on the lower half of the gap, just as in the case of Per a - 
ne'tna cyatheoides (de Bary, 6 Comp. Anatd, Fig. 132, and description, p. 285). 
Histologically the meristeles of the stock are uninteresting. The 
xylem is made up of regular tracheides, interspersed with few parenchyma- 
tous cells and with no definitely differentiated protoxylem. 
This is a characteristic of the meristeles of the stock among the 
Cyatheaceae, and except in that respect calls for no comment. The first 
lignification of the undifferentiated parenchyma in the young stock is on the 
inner side, as is represented in Fig. 5, which is made from a transverse 
section just below the apex of the young shoot. The stele is thus technically 
endarch as regards sequence of development, though no specifically marked 
tracheides of protoxylem appear to be found. Each meristele is enclosed 
in an almost complete sheath of phloem, which extends round the xylem 
on the inner and outer sides of the bundle, but is interrupted at the corners, 
so that two lenticules of phloem are found, one on each side of the mass of 
tracheides. The phloem is in turn surrounded by a parenchymatous peri- 
cycle of several layers and an endodermis with thickened cell-walls, often 
enclosing brownish contents. At the corners of the bundle the xylem comes 
directly into contact with the peri cycle. 
In the petiole the strands differ in structure from those of the stock. 
The leaf-trace strands leave the meristeles of the stock in quite simple 
fashion. In the case of the median leaf-trace strand, which departs first 
from the dictyostele at the fork below the gap, the oval strand shows 
a little hump or swelling on its outer surface. This gradually increases in 
size and rounds itself off from the parent stele as a plate of xylem sur- 
rounded by a sheath of phloem. The adaxial leaf-trace bundles leave the 
corners of two of the meristeles. They are at first simple in structure with 
a xylem-plate surrounded by a phloem sheath. In no case does a strand of 
the leaf-trace leave any gap in the xylem of the meristele from which 
