»»70 MR. W. C. WILLIAMSON ON THE HISTORY OF ZAMIA GIGAS 



lowermost margin of the layer retained in situ because wedged in that position, externally 

 1)V the bases of the bracts of the involucrum, and internally by the substance of the 



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pyriform peduncle. The smoothness of the surface of the peduncle, demonstrated by 

 several examples, clearly indicates that the connexion between it and the investing 

 cells has been very slight ; the detachment of the latter may have resulted either from 

 maceration in water readily severing this connexion, or from the tissue having been truly 

 dt5ciduous, and destined to be thrown off like many recent antheriferous structures. 



Attention has been directed to the radiating striae marking the outer surface of the 

 tunnel-shaped base of the lenticular disk (Plate LII. fig. 5): I have several specimens 

 demonstrating that at least the exterior of this part of the axis has been composed of 



elongated cells similar in appearance to those of the cortical layer; but they appear to 

 have formed a permanent part of the axis, being almost invariably found in situ when the 

 carbonaceous matter is preserved. Whether they occupied the whole diameter of the 

 peduncle, or only formed an external layer, I cannot determine *. Instead of being arranged 

 vertically to the surface of the axis, they are disposed longitudinally and in symmetrical 

 parallel lines, following the curves of the exterior of the axis ; their terminations are seen 

 on the upper surface of the lenticular disk, especially at its peripheral portion (fig. 6). The 

 exact relation of these cells to those of the outer layer is uncertain, but there is always 

 I remarkable break in the continuity of the tissues here, showing some important change 



in their arrangement In the undeveloped examples (Plate LIII. fig. 9) a thin series of 



the most superficial of these cells appear on the surface of the lenticular disk, converging 

 towards the base of the pyramidal axis, which they then ascend, and are continued in the 

 same manner to the extremity of the central mammillary apex of the corona. It thus 

 appears that at least the surface of the axis above the narrow base of the lenticular disk 

 has been composed of a series of elongated cells or tubes, arranged longitudinally and 



following the curves of the surface, and that a number of them terminated abruptly at 



or immediately beneath the upper surface of the lenticular disk. As seen in fig. 7, many 



of the superficial grooves caused by these tissues are more strongly marked than the 



reft, recurring at regular intervals. The undeveloped specimens indicate a similar 

 external contour. 



Along with the specimens described some others are found having a very different 



t'erior surface of the 



peet, but apparently belonging to the same plant. Pig. 2, Plate LII., represents 

 of them in the Scarborough Museum, of the natural size; it is a cast showing the 



ganism. It is a funnel-shaped body ; the hollow interior is 



abont an inch in depth, and rather more than half an inch wide at its fundus, enlarging 



about an inch at its upper part, where it suddenly expands into a broad disk, having 



of m ly 4 inches, exclusive of a circle of radiating appendages. The latter 



slight tendency to be recurved downwards. The entire surface is marked by 



gular radiating striae, and also by several grooves and corrugations, which 



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we strongest in the tubular portion of the specimen. Round its peripheral margin „. 

 the remams of a number of radiating appendages, each beine about an inch in length 



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thickness 



defined external cylinder about \ 



in 



