956 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
D. Two mature spores to show fissures and thickening of the spore- 
membrane. C.N. 1007. X 200. 
. 35. Part of a sporangium, to show layer of parenchyma lining the sporangial 
wall. Within this are mature spores, C.N. 1008. x 150. 
= 
re 
Figs. 36-39. Calamostachys Casheana. 
Fig. 36. Transverse section of the axis of the strobilus. In the middle is the central 
cylinder, with a large pith, surrounded by 6 vascular bundles. The structure 
is the same as in fig. 24 (Plate 80), from C. Binneyana (px., two of the proto- 
xylem-groups). There is a well-marked zone of radially arranged secondary 
xylem. Outside this are remains of thin-walled cells, and surrounding the 
whole is the well-preserved outer cortex. The outlines to the exterior mark 
the position of the sporangia. This is from the same preparation as photo- 
graph 16, on Plate 74. C.N. 1588. xX 70. 
Fig. 37. Section of a macrosporangium (that warked x in fig. 36), containing several 
macrospores (as at ma), and a large number of abortive spores (as at 6). 
There are slight remains of tissue lining the sporangial wall. C.N. 1588. 
A. Microspores from the tangential section of the same specimen. C.N,. 
1587. 
B. Macrospores and abortive spores. C.N. 1587. 
C 2 3 % C.N. 1588. 
All the above x 100. 
Fig. 38. Group of four sporangia from a tangential section, with the pedicel of their 
sporangiophore (sp.) between them. One is a microsporangium ; the other 
three are macrosporangia. Among the macrospores abortive spores are seen. 
Also shown in Plate 74, photograph 15. C.N. 1587. x 30. 
Fig. 39. Parts of two adjacent sporangia from a tangential section of the other 
specimen of this species. To the right is a microsporangium, containing 
microspores (mt) only. To the left is a macrosporangium, in which one of the 
macrospores (ma) and several abortive spores (b) are shown. C.N. 1025. 
x 100. 
PLATE 83. 
Figs. 40-444. Sphenophyllum plurifoliatum. 
Fig. 40. Obliquely transverse section of a moderately young stem. In the middle is 
the triarch primary xylem. The three protoxylem groups at the angles ( pz.), 
with their small, spiral or reticulated trachez, are clearly seen.. The more 
central primary trachez are pitted. About four layers of secondary wood 
