﻿TRUNK STRUCTURE. 79 



woody structure as extensive and compact as that of Cordaites. This specimen is 

 35 cm. in length by 25 cm. in diameter, and the curvature of the basal end and small 

 diameter of the medulla show that it is from the base of a distinctly columnar trunk. 

 Although the armor and cortex are mostly eroded away, some proximal ends of leaf 

 bases on one side prove very conclusively, in conjunction with the other characters 

 present, the cycadean nature of the specimen and show that the cortical parenchyma 

 was but slightly developed, or rather replaced by the heavy woody zone. This rem- 

 nant of armor, while not showing the original thickness, of course indicates that 

 periderm excision of the leaf bases had not progressed so far as often seen in various 

 existing cycads of columnar type. The unusual characters of the present specimen, 

 as well as the convenient form for handling, led the writer to have the upper end 

 polished, and the result was a most agreeable surprise. The very light outer 

 coloration was found to give way to more pronounced shades in the interior, which 

 bring out the larger structures with great clearness and beauty, and, as it happens, 

 in shades that render the photograph and the reproduction in the plate virtually 

 representations in natural colors. An extreme hardness and toughness not unlike 

 but exceeding that of chalcedony, as well as some doubt as to the advantage of 

 so doing, has, in the presence of so many other points pressing for solution, deterred 

 the writer from making thin sections from the trunk. However, with regard to the 

 special structural features that appear in the transverse section (plate xiv) it may 

 be noted that the successive woody rings closely abut, and that, as in the case of sec- 

 ondary rings or anomalous wood zones in the existing cycads, the outer ones are very 

 narrow; though the relative amounts of xylem and phloem can not be determined 

 either in the figure or by macroscopic inspection of the original specimen. Never- 

 theless, it appears more likely that secondary cambial formation has intervened and 

 resulted in the development in the cortex exterior to the initial woody cylinder of 

 a dozen or more of successive exterior collateral bundle systems, simulating annual 

 rings much after the manner of old trunks of Cycas and Macrozamia among the 

 modern cycads, but with extremely narrow medullary rays, resulting in as solid a 

 wood zone as if mainly consisting in a growth of secondary xylem from a persistent 

 cambial cylinder, as in conifers and dicotyls. The highest number of anomalous 

 wood zones recorded in the existing cycads is twelve in an old trunk examined by 

 Miquel. The even greater number and very complete lignification of additional 

 rings of growth in the present case thus give the medullar proportions and solidity 

 of cordaitean stems. 



On the other hand, there is a bare possibility that there has actually been a 

 persistence of the primary cambium with seasonal augmentation of the secondary 

 xylem. Should it be proven later that in any of the Cycadeoidese such a condition 

 is present, it would certainly indicate a most unexpected feature of these trunks, so 

 like cycads in all other respects. Such a dicotyledonous feature would, too, in con- 

 junction with the angiosperm-like arrangement of the bisporangiate strobili, repre- 

 sent an assemblage of advanced characters not found in any other group retaining 

 as many primitive features as the present. It is of much interest that Seward (149) 

 figures a fossil stem from India with Ptilopliyllum citlchense fronds attached, in 



