908 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
lower surface often contain dense masses of carbonaceous matter, which may represent 
some secretion formed during life. 
As the outer edge of the coherent disc is approached, we find that its upper surface 
becomes undulated, as seen in tangential section. Each elevation of its surface 
corresponds to the position of one of the free bracts, which here begin to separate 
from each other. The free portions of the bracts, as already stated, are of great 
length. They gradually taper off towards their tips, and their structure undergoes a 
corresponding simplification. 
In its lower region the free part of a bract is composed of the same tissues as are 
found in the coherent disc, arranged in the same manner. The secretory sacs (if 
that is their real nature) are especially conspicuous in this part. The upper 
extremity of the bract consists of sclerenchyma only, through which the fine vascular 
bundle can be traced for some distance. 
The free bracts are shown in longitudinal section in Plate 73, photograph 10, and 
in transverse section in photographs 12 and 13. In Plate 74, photograph 14, some 
of them are also shown in oblique superficial view. 
It need scarcely be pointed out again that the whole of the highly differentiated 
bract-system, so characteristic of fossil Calamarian fructifications, has nothing clearly 
corresponding to it among existing Eguiseta. In this fact we have a striking 
illustration of the general rule, that the Palseozoic Cryptogams known to us, were far 
more highly organized plants than their allies which are living in the present age. 
B. The Sporangiophores. 
The general form of the peltate sporangiophores, and their relation to the axis, 
have been described above. The pedicel consists of a zone of somewhat sclerotic 
cortical tissue, enclosing a single vascular bundle (see Plate 73, photographs 11 
and 18; Plate 81, figs. 29 and 30). Immediately below the peltate expansion, or 
head, which terminates the sporangiophore, the pedicel becomes broader, and here 
the vascular bundle forks into two branches, which lie in the same horizontal plane. 
Each of the branch-bundles forks again, and the four ultimate ramifications run out 
to the bases of the four sporangia, which are placed diagonally at the margin of the 
peltate head (see Plate 81, figs. 29 and 32). The parenchyma of the peltate portion 
is thin-walled ; the free external surface and edges are covered by a very charac- 
teristic layer of elongated, palisade-like, epidermal cells. This palisade-layer is very 
delicate, and is rarely perfectly preserved ; it is best shown in a specimen figured in 
a former memoir* (see also Plate 73, photograph 13; in Plate 81, fig. 29, only 
fragments of this layer are shown; in the tangential section, Plate 81, fig. 32, the 
layer is evident). 
The general outline of the peltate expansion of the sporangiophore, as seen in 
* Win.tamson, “ Organization,” Part XV., Plate 2, fig. 8 (C.N. 1000). 
