8 Ward Species of Oy&tdeoidea from M<tnjl<m<i 



the trunk, which varies with the species and more or less with different 

 specimens of the same species. One of the two sets of rows is usually 

 more distinct than the other, but the more distinct rows sometimes pass 

 upward from left to right and sometimes from right to left. The bases of 

 the petioles when present and well preserved often show at the surface 

 presented to view a row of pits all round parallel to the walls and at differ 

 ent distances from the margin representing the vascular strands. Other 

 such pits are sometimes present near the center. The petioles are fre 

 quently disarticulated at a natural joint, which may fall near or at the 

 summit of the scar, or it may fall some distance within the scar. In some 

 species there are two such joints separated by a node. Occasionally these 

 joints consist of a thin membranous diaphragm stretching across the 

 petiole, of firmer texture than the rest of its substance. Even where the 

 petioles are wholly absent the position of the joints or diaphragms can 

 sometimes be determined by a sharp ridge round the inside of the scar. 

 The walls are made up of the ramentum of two adjacent petioles. In some 

 cases these matted masses are so dense as to produce a simple homogene 

 ous plate on all four of the sides, which, where the petioles are wanting, 

 forms a deep, angled cavity of exactly the shape of a cross section of the 

 petiole. Usually the portion of the wall furnished by each of the adjacent 

 petioles can be distinguished by a junction line or commissure, visible 

 along the outer edge of the wall. This commissure sometimes takes the 

 form of an intermediate plate of a less dense consistency than the two 

 outer plates. In other cases this central plate is much thicker than the 

 two outer ones, which latter may be reduced to the appearance of thin 

 linings of the scars. In still other cases the central portion is more or 

 less open and cavitous. The walls vary from 1 millimeter or even less to 

 o millimeters or, in rare cases, 8 millimeters in thickness. 



The other class of organs that help to make up the armor are the repro 

 ductive organs. These are borne on all parts of the surface of the trunks 

 except, perhaps, in immediate connection with the terminal bud, which 

 is exclusively an organ of growth. They are scattered about with very 

 little order over the surface among the leaf scars. They are usually of a 

 harder substance than that of the foliar organs and better adapted to re 

 sist erosive influences to which the fossil trunks are exposed. Where the 

 trunks are worn, therefore, the reproductive axes are liable to protrude 

 somewhat. Viewed from without, they usually present an organ with an 

 elliptical cross section, the longer diameter being nearly horizontal, vari 

 able in size, but always larger than the leaf scars. The central portion is 

 often wanting, and a funnel-shaped cavity less deep than the leaf scars 

 takes its place. When the central portions are present they show mark 

 ings having the form which the outer ends of the essential organs pre 

 sent, which is very variable and usually obscure. Surrounding the cen 

 tral portions are several rows of open scars arranged concentrically. 

 These scars are sometimes triangular, quadrangular, polygonal, or nearly 

 circular; but the most of them, especially the outer ones, are somewhat 

 crescent-shaped, having the concave side toward the center. The inflo 

 rescence is a spadix surrounded by an involucre consisting of the eomvn- 



