﻿276 AMERICAN FOSSIL CYCADS. 



2a. Parallel to and quite three centimeters beneath preceding section. Cuts peduncle 

 and surrounding bracts only. S. 482. 



2b. Parallel to and several centimeters beneath the preceding section. Passes through 

 central region of the large peduncle, of flattened barrel-shape, and beneath the insertion of 

 most of the bracts. S. 483. 



2c. Parallel to and several centimeters beneath preceding section. Cuts peduncle and 

 leaf bases beneath all the bracts, and but a short distance above insertion on cortex. S. 484. 



The photographs of the present plate, although from two different strobili, virtually 

 constitute a complete series of transverse sections. Taken as the complement of the longi- 

 tudinal sections shown in the upper photograph, plate xxxiv, and photograph 4, plate xxxix, 

 they afford a complete pictorial view of the macroscopic features of the bisporangiate stro- 

 bilus. Compare with the outline figures 74 and 75, pp. 149-151. 



Plate XXXVI. Cycadeoidea dacotensis. Serial sections through 

 a bisporangiate strobilus. 



All the photographs of this plate are twice natural size. 



Photograph 1. — Longitudinal section so cut that in the once-decurved frond to the right 

 of the ovulate cone none of the synangia-bearing pinnules appear. Instead, the entire space 

 between the ascending and descending limbs of the rachis is closely packed with synangia. 

 To the left of the cone a few of the synangia are seen to be borne on pinnules attached to 

 the microsporophyll rachis. 



Photograph 2. — Longitudinal section parallel to the preceding at a distance of several 

 millimeters, and so cut that the pinnules of the microsporophylls on both sides of the cen- 

 tral cone are successively cut throughout their entire length. (Planes of the serial trans- 

 verse sections 2a-2d indicated by the respective lines a-d. Likewise planes S. no and S. 302 

 indicate the position of the two sections at right angles to the preceding, but cut from 

 another of the cones borne by T. 214, and shown in enlarged view in the photomicrographs 

 2 and 3 of the following plate.) 



Photographs 2a, 2b, 2c, and 2d. — Serial transverse sections cut in the respective planes 

 indicated by a, b, c, and d, in photograph 2. It is especially to be observed that in photo- 

 graph 2a the disk is divided into discrete fronds, while in photograph 2b, owing to slight 

 obliquity, separate fronds are to be seen on the left, but not on the right. The latter section 

 hence indicates that the exact height at which the disk divides into fronds is on a level with 

 the summit of the ovulate cone. Compare with outline figures 72 and 73, pp. 145-147- 



Plate XXXVII. Cycadeoidea dacotensis. Longitudinal Sections of Bisporan- 

 giate Strobilus. (I, T. 214. Structural details.) 



Photograph 1. — S. 83. X 8. Longitudinal section through upper portion of ovulate cone 

 and the decurved limb of an appressed microsporophyll. 



Photograph 2.— S. 302. X 8. Tangential section of strobilus passing through region 

 of closely packed synangia near ascending limb of a rachis in a position approximately ver- 

 tical to line marked S. 302, in photograph 2, plate xxxvi. The pinnules (s) of the once- 

 pinnate microsporophylls, as folded in lengthwise, are cut transversely in pairs and the 

 synangia are seen to be attached pendently well to the side of the heavy median nether keel. 



Photograph 3.— S. no. X 8. Section passing radially outward and upward through 

 the folded once-pinnate microsporophylls at such an angle as to cut a pinnule (p l hori- 

 zontally throughout its entire length. The approximate position of the section is vertical 

 to the line S. no, photograph 2, plate xxxvi. Taken in conjunction with the preceding 

 tangential section the present section pretty clearly shows the form of the pinnule and the 

 distribution and attachment of the synangia in two lateral pendent rows, f and f, two 

 adjacent fronds; />', pinnule borne by frond 1; p 2 , pinnule borne by frond 2 and cut off 

 obliquely ; />*, another obliquely cut pinnule either borne by frond 2 or an adjacent frond. 



In the present section the pinnule (p 1 ), as attached to the rachis of the frond (f) of 

 the disk, bears on its left side the row of five synangia seen to the left of the photograph, 



