102 CYCADEAE, MEDULLOSEAE. 



have enclosed a medullary strand of vascular bundles, since I find in a 

 section obtained from a specimen from Chemnitz two groups of vessels in 

 the centre of the ring which have escaped the general destruction. This 

 point, as well as the question of the longitudinal course of these elements, 

 can only be cleared up by further researches, but we may have to wait 

 some time for these in the present scantness of material. It is greatly to 

 be regretted that the discovery of the silicified stems in the Rothliegende 

 of Chemnitz occurred so early in the last century, for the locality is now 

 nearly exhausted, and the most precious material has been frittered away 

 and spoilt to make ornaments, and to furnish the mineralogical trifles in 

 vogue at that time. 



If we now examine the outer ring of wood in Medullosa stellata more 

 closely, we become aware of the remarkable fact, first disclosed by Goppert 

 and Stenzel, that the riflg does not consist, as had long been supposed, of 

 two consecutive annular secondary growths, as in Cycas, but that it is 

 composed of a variable number of plate-rings, which are narrow and more 

 or less elongated on the transverse section and together simulate a peri- 

 pheral woody circle (Fig. 6, A}. The intervals mentioned above and 

 formerly taken for broad medullary rays are simply gaps between the 

 single plate-rings of the circle of wood. The linear partial pith of these 

 plate-rings appears on a superficial examination as the boundary of the 

 two consecutive secondary growths ; it is of course bounded by woody 

 tissue on its outer and on its inner side, and this is succeeded on both 

 sides by normal bast-masses which are traversed by many transverse 

 sections of fibre-cells. Disturbances, curvatures, and the like are quite 

 common in these plate-rings, as in those of the inner pith, and may 

 naturally be referred to the pressure to which the developing masses of 

 secondary tissue were everywhere exposed in the middle of the body of 

 the parenchyma. It might be supposed that there was another normal 

 woody cylinder outside the one which has just been described and which 

 was formed of the plate-rings, and that we have therefore only the 

 pith of the stems before us. That this is not the case however is 

 proved by another species, M. Ludwigii, brought by Ludwig from the 

 Uralian Steppe and described by Goppert and Stenzel. The surface, which 

 is preserved in this stem, is covered with somewhat crowded roundish 

 impressions, which these authors unhesitatingly compare with the leaf-scars 

 of the stems of Cycadeae. From the figure alone I can form no opinion 

 on the point ; but the star-rings and plate-rings in this species are all 

 confusedly and irregularly disposed, and no peripheral woody cylinder is 

 formed from the plate-rings. All this seems to show, as Goppert and 

 Stenzel very justly remark, that the anomalies in the growth of the stem 

 in Medullosae remind us much less of the conditions of growth in the 

 genera Cycas and Encephalartos than of those of Sapindaceae, and this is 



