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ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 935 
they arise from the upper surface of the coherent disc near the axil. The extent to 
which they adhere to the surface of the disc varies greatly ; in some cases they 
become free at once; in others they do not become wholly free until the point is 
reached where the bracts themselves begin to separate from one another.* It does 
not appear, however, that there was ever more than a single verticil of sporangio- 
phores belonging to each verticil of bracts; appearances to the contrary seem to be 
due to the varying degree of adhesion between the two organs (Plate 85, fig. 54). 
A transverse section of the strobilus may show one or two circles of sporangia 
between two whorls of bracts ; sometimes even a part of a third circle is present. 
The same variations are observable in tangential sections. These differences can only 
be explained by the fact that the sporangiophores overlap each other, so as to bring 
their sporangia to different levels. Where additional sporangia appear within the 
same internode, their position is both exterior and superior to those of the first circle 
(see Plate 76, photographs 25 and 26, and compare with the figures in WILLTAMSON, 
Part XVIII). Hence the longer pedicels must have passed to the outside of the 
sporangia borne on the shorter ones, as is often well shown both in transverse and 
tangential sections.t 
The longer sporangiophores considerably exceed an internode in length, for we find 
sporangia belonging to two successive verticils of bracts appearing in the same trans- 
verse section.{ 
The sporangiophores follow the upward curvation of the bracts, keeping at a little 
distance from their superior surface. Each bears at its end a single sporangium, 
which is attached in a very characteristic manner. The pedicel bends inwards at its 
extreme end, and the sporangium is suspended from it, so as to hang almost parallel 
to the pedicel, occupying a position rather like that of an anatropous ovule in relation 
to its funicle (Plate 76, photograph 25 ; Plate 85, figs. 57 and 58). 
This short account of the general morphology of the strobilus may suffice as an 
introduction, considering the full descriptions which have already been published. We 
will now proceed to consider its internal structure. 
The Axis. 
The axis of the strobilus is traversed by a solid vascular cylinder, of which only 
the wood retains its structure. In the larger specimens the wood forms a very 
bluntly triquetrous strand.§ 
Each of the obtuse corners is prolonged into two projecting points, with a marked 
bay between them. The smallest trachee are at the points, so that we may 
* Sce Wiiiauson, “ Organization,” Part V., Plate 5, fig. 28; Part XVIII, Plate 26, fig. 7. 
+ Wititamson, loc. cit., Part XVIIL., Plate 26, fig. 2; and Plate 25, fig. 8. 
t Wiuriamsoy, loc. cit., Part V., Plate 5, fig. 28. 
§ See Wituiamson, loc. cit., Part V., Plate 5, fig. 29; and Part XVIII., Plate 25, fig. 1. 
MDCCCXCIV.—B, 6 D 
