OF CALAMITEAN STROBILUS. 253 



be traced up to the two well-marked sporangiopliores h" Ji^' . 

 If we proceed right and left from this starting-point, owing 

 to the obliquity of the section, we can trace the gradual 

 divergence of the sporangiophores from the central axis, 

 and their isolation amidst the masses of sporangia which 

 they have supported — also the contraction of what I 

 have termed the primary peduncles of the bractigerous 

 disk into mere prominent longitudinal ridges on the ex- 

 terior of the central axis, like those on the stem of a Cala- 

 mite, whilst the large pyriform cavities, in like manner, 

 become deep grooves separating these ridges. In this 

 figure little attempt has been made to delineate the compli- 

 cated and interrupted outlines of the sporangia, i i, except 

 at the peripheral margin, /, where their distinct continuity 

 shows that we possess the outermost portion of the stro- 

 bilus. In the interior of the structure, the arrangement 

 of these sporangia has been much disturbed, apparently by 

 inequalities in the mutual pressure to which they have 

 been subjected, resulting from the growth of the spores. 



Fig. 5 represents the central portion of a transverse 

 section made at a higher point than the last, corre- 

 sponding to the line y y in fig. 13. The cylindrical axis 

 surrounding the medulla (a) is now more sharply de- 

 fined, owing to the absence from this internodal portion 

 of the bractigerous disk. The homologues of the bases 

 of the ten primary peduncles of fig. 4 are identified by 

 the two small canals in each {c, c), which here approach 

 the outer surface of the axis : we thus see, as I have 

 already suggested, that these primary peduncles are merely 

 nodal prolongations of ten somewhat rounded, project- 

 ing ribs running longitudinally along the exterior of the 

 central axis; these ribs, becoming increasingly promi- 

 nent as they approach the node, both from above and 

 from below, gradually converge, and at length coa- 

 lesce, so as to enclose the intermediate grooves, which 



