695 



In tr 



FROM THE SECONDARY ROCKS OF BRITAIN. 



"all the specimens of Cycadites hitherto found in the Isle of Wight agreed in havin" an 

 elliptical outline, unaccompanied with any inequality in the woody ellipsis, and also in 



having a bud in the axilla of each leaf; in these respects differing from the GgcadU* of the 



Isle of Portland, and from all the recent species of Cycadea with which we aiv acquainted, 

 which have a circular outline and only scattered buds." Besides the specimens examined 

 by Mr. Brown, I have obtained several additional examples of the same species, as well a> 

 specimens of other species, which have enabled me to make a more complete examination 

 of their structure than the materials at his disposal permitted him to make. Those reveal 

 structures in the organs of fructification as well as in the stem, which require that tiny 

 be separated into a distinct genus which cannot be classed under any of the recognized 

 subdivisions of the Order, but is the type of another well-marked group of equal value with 

 the others. To the genus I have given the name Bennettites, after my distinguished 

 colleague, to whom, as my friend, instructor, and guide, I owe a debt I never can lulh 



estimate. 



In the remarkable external features noticed by Mr. Brown all the species agree. 

 They have an elliptical axis and a bud in the axils of many, not of all, of the leaves. Thi 

 stems are short. The oval medulla is composed of large subspherieal c llular tissue, free 

 from separate woody bundles, but penetrated everywhere with gum-canals. The pith i- 

 surrounded by a single cylinder of wood, the minute structure of which would h de- 

 scribed as scalariform; but it is certainly different from the typical form of this found in 

 living ferns, or in the arborescent Zycopodiacece of the Coal-mea-ures. 

 sections the wood-cells have the round or sub quadrangular form of the til.ns of livinj 

 Cycads and Conifers. Longitudinally they exhibit transverse bars, or, rather, oval spa ee 

 but when these markings are seen in section they are found to be external to the cell-wall, 

 or, rather, equally related to the outside of the contiguous walls of two cells, as in the dis- 

 cigerous tissue of gymnosperms. This cannot be described as a transition from disci- 

 gerous to scalariform tissue; but, indeed, from the nature of the two tissues (the on. 

 internal, the other external to the wood-cell), it is not possible that there can he an;, trans 

 ition between them. The wood is abundantly penetrated by true medullary rays I h. 

 wood is composed of two layers, an outer and inner, looking, in transverse section, like to* 

 true wood and the accompanying « inner stratified cortical layer " of Link seen m recent 

 trunks of this order; but in longitudinal section they are seen to be both prosenchy- 

 matous structures. Beyond the wood is a zone of cortical parenchyma similar in struc- 

 ture to the large medulla, and, like it, everywhere penetrated by gum-tube,. ±rom t m 

 spring the leaves ; the permanent bases of the -petioles form an investing cemmg U > «» 

 stem of considerable thickness. The vascular bundles which supply the lea™ ha 

 origin in the woody axis ; but their relation to that axis is n, « ^~£ J 

 * other Cycadece. They rise, in all the known members of the umer, jn 

 ^e cylinder of wood, as Lndles of small size and, p« = h ^^» ^ 



neons cylinder, and then through the cortical P arench ^\Xn te l direction parallel to 

 ^ning for a short distance, at least in some genera, in a hmizonu i ^ ^ ^ 



the periphery of the stem, they pass into the petiole of each ^ * ^ 



Cycads the vascular tissue for each leaf springs from the woody cylinder fr 



