938 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
The sporangiophore, in its lower part, is a small cylindrical pedicel, of simple 
structure. Its diameter near the base is only about *15 millim. It has a well- 
marked epidermis, beneath which there is sometimes a rather sclerotic hypodermal 
layer.* The delicate inner tissue is more or less disorganized. The xylem of the 
vascular bundle, which here consists of two or three trachez only, is placed towards 
the adaxial surface. 
As we follow the sporangiophore upwards, we find a gradual change in its structure. 
Certain of the epidermal cells become enlarged. Sometimes one cell on each side 
projects beyond its neighbours, giving a winged appearance to the transverse section. 
As we approach the sporangium, the sporangiophore grows thicker, attaining a 
diameter of about ‘4 millim. In this part all the epidermal cells of its outer or 
dorsal surface are enlarged. The transverse section is here approximately semi- 
circular (see Plate 85, fig. 57). The vascular bundle contains many more tracheze 
than in its lower part ; we can now see clearly that while the xylem, as a whole, is 
situated towards the inner surface (an indication that the bundle was collateral), its 
smallest trachez are directed outwards. This is constantly the case wherever the 
preservation permits the structure to be clearly seen. It appears then that in the 
sporangiophore, as in the leaf, the xylem was centripetal. All the trachee are 
spiral. 
The sporangiophore bends over at its extremity, towards the axis of the strobilus. 
Here the sporangium is attached to it with a fairly broad base. The xylem preserves 
its full thickness to the last, and comes to a sudden end, being obliquely truncated 
where the cavity of the sporangium begins. The thin-walled tissue surrounding the 
xylem extends further into the sporangium, and gradually thins out along its walls 
(see Plate 85, fig. 58; Plate 76, photograph 25, and more especially WiILLIAMson, 
Part XVIII, Plate 27, fig. 16). 
The sporangium, as already mentioned, lies back nearly parallel with the pedicel, 
with the flat side of which it is in contact (figs. 57 and 58). 
In our specimens the wall of the sporangium is but one cell in thickness, except 
near the base. The wall is similar in structure to the epidermis of the adjoining portion 
of the sporangiophore. M. ZEiLLER has suggested several questions as to the sporangial 
wall, which we have endeavoured to solve.t He enquires whether there is a regular 
diminution in the size of the cells of the wall, as the distance from the pedicel 
increases. There is certainly a diminution, but itis not quite regular. We often find 
a constriction near the base of the sporangium, which we may take as marking the 
limit between the sporangial wall and the epidermis of the pedicel (see photo- 
graph 25, and figures above cited). Beyond this constriction, large cells, just like 
those of the epidermis, recommence. They gradually diminish in size, as we trace 
the sporangial wall towards the free end, but soon their diameter becomes uniform. 
* Wittiamson, loc. cit., Part XVIII, Plate 28, fig. 15. 
+ Loc. cit. p. 22. 
