552 
Bower.—On the Primary Xylem, and the 
DESCRIPTION OF FIGURES IN PLATES XLV AND XLVI. 
Illustrating Prof. Bower’s paper on Primary Xylem, and the Origin of Medullation in the 
Ophioglossaceae. 
PLATE XLV. 
Fig. i. Transverse section through the base of a root-bud of Ophioglossum palmatum , showing 
that the stock is medullated from the first. The elongated tracheides belonged to the parent root : 
the ring of tracheides marks the base of the axial stele, x 125. 
Fig. 2. Transverse section of the base of the stock of Ophioglossum reticulatum , showing 
a protostelic state. A few parenchyma cells are present in the otherwise solid xylem-core. x 144. 
Fig. 3. A section a little higher up, showing an initial state of a parenchymatous pith, x 144. 
Fig. 4. A section still higher, showing the xylem-ring open, and the pith in communication 
with the conjunctive tissue, x 144. 
Fig. 5. A drawing of the central region of Fig. 3 on a higher scale, showing that there is no 
exact limit between the parenchyma nests of the xylem and the pith. 
Fig. 6. Transverse section of the base of the stock of a weak plant of Boirychium Lunaria, 
from the Breadalbane Hills. The endodermis is already well marked : a root is passing off to the 
right. The stele is a protostele, but parenchyma cells are scattered through the otherwise solid 
xylem-core. x 125. 
Fig. 7. Section of the same plant higher up, showing a pith connected through a gap in the 
xylem-ring with the conjunctive tissue. The endodermis shows irregularity of its cells, and 
a slight involution opposite the gap in the xylem-ring. The narrow arm of tracheides which 
projects outwards is the first leaf-trace, of which the gap defines one margin, while it is still 
connected with the xylem of the stele by the other margin, x 125. 
Fig. 8. Section of the same plant at the departure of the first leaf-trace. The xylem-ring 
is still open, and thus the pith communicates with the conjunctive tissue. But the endodermis, 
which is involuted but not interrupted at the passage outwards of the leaf-trace, still forms a com¬ 
plete barrier, shutting in the stele. The cells of the pith to the right are clearly sister cells with 
the tracheides surrounding them, x 125. 
Fig. 9. Departure of the trace of a larger and higher leaf of the same plant. The trace 
consists of more numerous tracheides, the xylem-gap is wider, and the pith more massive. But 
the endodermis is still a complete sheath, and has shown no interruption from the base of the 
plant. It surrounds still the outgoing leaf-trace, but a band of endodermis is seen internal to 
the leaf-trace, and it is specially to be noted that it arches strongly inwards into the wide xylem- 
gap. x 125. 
Fig. 10. Transverse section of the stock of a small plant of B. Lunaria from the Breadalbane 
Hills, from a series cut by Dr. Lang. It shows the departure of the fourth leaf-trace. Up to 
this point the endodermis has been a complete barrier, but now it appears interrupted for the 
first time, at points outside the departing trace. The pith contains scattered tracheides, showing 
the condition of a ‘mixed pith’. It is to be noted that where tangential divisions have doubled 
the cells of the endodermis it is sometimes the inner, sometimes the outer of the sister cells that 
bears the characteristic marking. There is no internal endodermis. x 125. 
Fig. 11. Transverse section of the stem of a plant of B. Lunaria which has produced numerous 
leaves, cut at a level just below the apex. The secondary thickening is beginning, but the tracheides 
already matured are regarded as representing the primary wood. The limit of the pith is here very 
ill defined, 'x 125. 
Fig. 12. Part of a transverse section of a stem of B. Lunaria, showing the departure of a leaf- 
trace. An isolated tracheide lies in the middle of the parenchymatous tract connecting the pith 
with the outer conjunctive tissue, x 200. 
Fig. 13. The inner margin of the xylem in a sporeling of B. virginiamim, showing two 
tracheides surrounded by pith, and almost detached from the xylem-tract. x 200. 
Figs. 14-16. Transverse sections of the inner margin of the xylem in plants of B. ternatum , 
showing isolated tracheides or groups of them lying free in the parenchymatous pith, x 200. 
