other specimen (figs. 6-8) indicates; and the general aspect of the involucrum (ti 



->D 



MR. W. C. WILLIAMSON ON THE HISTORY OF ZAMIA GIGAS. 669 



fourth of an inch in diameter (fig. 7), and from the centre of this there arises a small 

 terminal mammillary projection, rather more than the eighth of an inch in height and 

 breadth; to this cup and its terminal mamilla I would give the provisional Dame of tin 

 corona. 



Two specimens in my cabinet exhibit the lenticular disk, with its pyramidal axis and 

 corona, in a much less completely developed state. One of these is in the example 

 fig. 5. A vertical section is shown in fig. 9. In this state the corona is well del eloped ; 

 the mamilla is more acute than in fig. 6; but the pyramidal axis is almost wholly 

 wanting, the corona being nearly sessile upon the depressed centre of the lenticular 

 disk. This obviously appears to be a less developed condition of the organ than 1h< 



ests the same idea, it being much less globular than is the ease with fig. C>. These 

 younger specimens afford almost absolute proof that the corona is the terminal portion 

 of the central axis. I have now seen four of these rare examples, and they all bear the 

 strongest marks of terminal completeness. It mav,be worthy of note that the specimen 

 (figs. 10, 11, 12), the only one I have seen in which the pyramidal axis is fully developed, 

 is the only one also in which the surface of the pyriform axis is shrivelled and e rru- 

 gated, instead of smooth, as if the organ had fulfilled its mission and was drying up. 



Having thus ascertained the form of the axis, we may now turn to some anomalous 

 features in its structure. Attention has been drawn to the ring of radiating cells at the 

 base. These are arranged like the cells of the honeycomb, each one being in turn the 

 centre of a surrounding group of six others (fig. 10); but they are often so com] eased 

 that it is only under favourable conditions that this arrangement can be deterin.n. I; 

 nevertheless it is an unquestionable fact. These cells appear to have formed a cortical 

 layer, arranged vertically upon and extending over the entire surface of the pyramidal 

 axis, having a probable thickness of from half to three-quarters of an inch at the tower 

 and central portions, and becoming thinner on approaching the constricted part o fee 

 axis, and most probably disappearing before reaching the funnel-shaped base of the lenti- 

 cular disk. I infer that it was coextensive with that part of the pyr form axis oiwlm h 

 the cast in the specimen, fig. 7, exhibits an uninterruptedly smootl 

 invested a great part of that surface, was shown by a specimen formerly m he pos^ 

 of M, Janfes YaL, and now, I believe in the conection £^J^* 

 Paris, as also in one in Mr. Ripley ' s cabinet ; and as all the specim 

 caan Se in the tissnes forming the surface of *<+.«? ^JtS K 



the funnel-shaped base of the lenticular di k • J «^°V, , , 



surface. That it 



D 



appear on 



appear on ttte lunnei-snapeu ua, c >» ~~ —-- concerned. Each 

 point this layer of cells thinned out, so far as «£**-££ smooth sur&ce „ the 



cell was in close contact, at its inner extremity (% 11,- ^^ , 

 pyramidal axis. Externally it seems to ha>e presented a 



crenulated outline to the vertical section of this tissue. represented in 

 This structure is invariably seen at the base of each in lucruni « ng ^ ^ 



%*• 3 & 6 (Plate LIL). I conclude that these cortica jd tor • J ^ ^ 



deciduous, being very easily detached from the ^°°th ^ ^^^ fa „nly the 

 the ring which is so invariably preserved round the base 



