﻿266 AMERICAN FOSSIL CYCADS. 



Plate XV.* Wood Structure of Cycadeoidca Wielandi. T. 393. 



Photograph I. — S. 255. X 5- Longitudinal tangential section through wood, showing 

 a portion of the cylindrical trellis of collateral bundles and the meshes in which the leaf 

 traces arise; the xylem elements of the latter being superior, the phloem inferior. 



Photograph 2. — S. 261. X 5- Transverse section through two adjacent "wedges" or 

 collateral bundles of the woody cylinder, showing the opening or medullary mesh between 

 and a horse-shoe bundle entering the cortex. The latter may arise in a mesh farther down 

 beneath the plane of the section. 



Photomicrograph 3. — S. 255. X MO- Enlarged view of a portion of figure 1, showing 

 more or less distinctly that the xylem of the woody cylinder is mainly composed of scalari- 

 form tracheids. Medullary rays one, seldom two, cells thick and one to fifteen cells high, 

 with intervening wood one to five cells thick. 



Photomicrograph 4. — S. 255. X 125 (?). A portion of same section as the preceding, 

 which cuts the xylem nearer the medulla, where the ray cells are relatively larger and the 

 tracheids smaller than further out towards the cambial line. 



Plate XVI. Structure of Woody Cylinder and Peduncle Trace in C. Wielandi. 

 T. 393- (Cf. text-figures 39, 40, etc.) 



Photomicrograph 1. — S. 260. X 15c Transverse section through xylem of one of the 

 collateral bundles of the woody cylinder and an adjacent mesh, showing in part the origin 

 of the xylem of a leaf trace. From position marked x in photograph 5. 



Photomicrograph 2. — S. 260. X about 200. Transverse section through phloem of 

 collateral bundle of woody cylinder. 



Photomicrograph 3. — S. 261. X 150. Transverse section through xylem of a cylindrical 

 bundle of the cortex, known to pass on and enter the peduncle of an ovulate cone. The 

 indistinctly preserved zone (c) crossing near the upper edge of the photograph is the cambial 

 region and beyond are a few of the cells of the phloem rays. 



Photomicrograph 4. — S. 261. X 150. Transverse section traversing the distal xylem, 

 the cambium, and the proximal two-thirds of the phloem of the same peduncle trace shown 

 in the preceding photomicrograph. Note the similarity of the xylem and the phloem struct- 

 ure of the peduncle to that of the woody cylinder of the trunk. The main differences con- 

 sist in the large proportion of phloem in the peduncle trace, and the smaller size of its 

 xylem and phloem elements. Further out the heavy-walled elements of the peduncular 

 phloem diminish greatly in number. 



Photograph 5— S. 247. X 3-33- Transverse section of trunk extending from the 

 medulla through the woody cylinder, the cortex, and the basal armor, c, Cambium of wood 

 cylinder; r, ramentum seated on outer cortex. At x is indicated the location of the xylem 

 area shown by photomicrograph I. Crescentic bundle emerging from between the two 

 woody wedges is a leaf trace, and the brokenly concentric bundle traversing the middle region 

 of the cortex a peduncle trace similar to that shown by the photomicrographs 3 and 4. 



Photograph 6.— S. 243. X 3-33- A peduncle trace cut transversely in its passage 

 through the outermost cortex, together with the leaf trace beneath to which it is axillary. 

 This bundle enters an ovulate cone from which various sections were cut. Note the distinct 

 cambial line and the width of the phloem, about four times that of the xylem. (For detailed 

 structure see photomicrographs 3 and 4.) 



Plate XVII. Transverse Thin Section through Armor of Colorado, Freeze- 

 out Hills (Wyoming), and Black Hills Cycadeoidean Trunks. Twice 

 natural size. 



Photograph I. — Cycadeoidea nigra. Peduncle and four of the five very large surround- 

 ing bracts appearing at the level of this section. 



Photograph 2. — Cycadeoidea nigra. Two adjacent leaf bases with axillary peduncles. 

 The two lowermost and oppositely-borne bracts of the upper peduncle are visible, but the 



*The reader should note that these and the succeeding heliotypes showing structure will readily admit 

 the use of a strong reading glass or hand lens. 



