ANATOMY AND AFFINITY OF CERTAIN RARE AND PRIMITIVE FERNS. 369 
Fertile pinnae of J. scalaris and J. verticalis have been examined. In both species 
the sporangia are distributed chiefly along the veins, but a few are inserted on the 
general pinna-surface (text-figs. 3 ( c ), ( d ), 4 (a)). There is no definite sorus and no 
indusium. The general absence of sporangia from the distal portions of the veins is 
probably a consequence of the membranous condition of the pinna-margin. 
The young pinna is completely covered by hairs, but the upper surface of the 
mature pinna is naked. The upper epidermis is strongly cuticularised, the mesophyll 
is well ventilated, and the protruding stomata are restricted to the lower surface 
(text-fig. 7). The general construction is indicative of specialisation under xerophytic 
conditions. 
In passing from stem to leaf-base the undivided trace of a well-developed leaf is 
accompanied for a short distance by the abaxial strap of parenchyma (fig. 9), but 
in the base of a reduced leaf the ground-tissue is uniformly sclerotic. The typical 
leaf-trace appears in transverse section of the leaf-base as in fig. 9. The xylem is 
a curved strap with marginal protoxylems. The phloem is on its abaxial face. 
As the petiole is ascended the phloem spreads adaxially until, in the rachis, it has 
surrounded the xylem (fig. 10). The pinna-traces are of marginal origin. The traces 
of the reduced leaves are of variable construction ; the phloem is ill-defined, and the 
xylem is on a reduced footing. These points are demonstrated in fig. 7, which shows 
a reduced trace in section through the leaf-base. The large leaves are of uniform 
construction, and their tissues are well differentiated, but the occasional small leaves 
show marked irregularities of form and construction, and their tissues are typically 
ill-defined. These facts lend support to the belief that the small leaves of Jamesonia 
are reduction forms consequent on mal-nutrition under xerophytic conditions. 
Sporangia. — The continued apical growth and slow differentiation of the leaf 
made it easy to follow the sporangial development in detail. The crowded sporangia 
are initiated in a “simple” condition astride the veins, and in transverse section of 
the pinna appear as in fig. 21. Occasional sporangia are inserted on the general 
surface between the veins, and in the mature pinna the “ Acrostichoid ” condition is 
pronounced (text-figs. 3 (c), ( d ), 4 (a)). The “ simple ” condition is maintained 
throughout the early stages of development (fig. 22), but there is a sudden change to 
a “ mixed” condition when the sporangia begin to elongate (fig. 23), and in the later 
stages of development the “mixed” condition is strongly marked (figs. 24, 25). A 
“gradate” condition has not been found at any point in the development of the 
sporangia, but the transition from the “simple” to the “mixed” state is 
always sudden. 
As will be seen from figs. 11, 12, 17, the slender sporangial-stalk consists of three 
rows of cells. The capsule is lopsided, one cheek being flattened, the other bulging 
(fig. 13). This lopsidedness seems in no way referable to the position or orientation 
of the sporangia, and when most prominent is usually accompanied by irregularities 
of the annulus. As is shown in the side, front, and expanded views of sporangia 
