﻿268 AMERICAN FOSSIL CYCADS. 



Figures 1-5. Dion edule. X 40. 



1. From near seat of leaf base. The annular and spiral tracheitis lie on the inner side 

 of the bundle, separated from the scalariform elements of the xylem (Holztheil) by thin- 

 walled tissue. Scalariform cells (centrifugal xylem) ranged radially in rows separated by 

 medullary rays, as in photograph I. 



2 (above i). Spiral cells (or protoxylem) surrounded by thin-walled tissue which 

 separates the centrifugal and centripetal xylem. 



3 (above 2). The centrifugal xylem is markedly diminished; the centripetal xylem 

 correspondingly increased. 



4. Xylem in three groups, the two lower centripetal. 



5 (above the preceding). Only three cells of the centrifugal xylem remain. 



Figure 14. — Cycas revoluta. X 40. 



Transverse section of a root bundle, showing a further example of the mesarch bundle 

 characteristic of the Cycadales. Development of sclerenchyma in the phloem is much as in 

 the fossil leaf-base bundles shown in photomicrographs above. 



Plate XXI. Cycadeoidea Wielandi (T. 393). X 0.33. 



Two views of a remarkably preserved specimen bearing numerous ovulate cones from 

 which various sections have been cut. The lines at upper c of photograph 1 indicate the 

 seed-bearing summits of four of the cones preserved entire, while at lower c another such 

 a summit is cut away; and at j two more such are cut, a portion of the summit of cone 

 to the left remaining with the seeds plainly showing on the horizontal saw cut. 



At b, photograph 2, owing to the breaking away of the armor near the cortex, the 

 bases of numerous peduncles may be seen ; five are marked. Although not thus thickly set 

 with fruits all over its lateral surface, the present trunk bears several such closely set 

 groups of cones ; whilst no considerable area at any point from the base to near the summit 

 is sterile. The seeds of the strobilus at 5 contain a preserved pre-embryonal stage like those 

 cut from yet another strobilus of this trunk and illustrated on plate xxx. The strobili 

 borne by the trunk illustrated on the succeeding plate xxn, while of the same outer appear- 

 ance as the present, are slightly more advanced in growth, a few of the seeds containing 

 young dicotyledonous embryos. 



Plate XXII. Cycadeoidea Wielandi. Entire Trunk and One of Its 

 Numerous Cones in Longitudinal Section. 



Photograph I. — T. 131. X 0.5. A finely preserved trunk bearing many ovulate cones 

 with seeds approaching maturity, and a lesser number of either young or abortive cones. 

 f, receptacle of a shed or non-preserved cone with surrounding bracts yet present; f", two 

 cones broken away during erosion, with a portion of the basal infertile pedicel series yet 

 remaining; f", four cones eroded down to the surface of the armor, in this instance about 

 or a little beneath the level of the lowermost seeds; y, three of the dozen or more very 

 young cones, in some cases known to be simply ovulate and to be regarded as having aborted 

 or else as belonging to a later and sparser series of fructifications than the seed-bearing 

 cones present, the latter unquestionably representing the culminant fruit-producing period 

 in the life of this cycad ; s (over lower arrow), the ovulate strobilus shown in figure 2 in 

 its natural position, this photograph having been made before the cone was cut out by a 

 cylindrical drill. 



Photograph 2. — S. 416. X 5- Longitudinal section of the small ovulate strobilus cut 

 from its natural position on the trunk as denoted by the arrow s, in photograph 1. e (upper 

 arrow), seed with dicotyledonous embryo preserved, cotyledons being similarly present in 

 the lowermost seed on the left-hand side of the strobilus ; s, traces of hypogynous staminate 

 disk; b, bracts; 1, leaf bases; d, layer of developing periderm C ?) marking the line at which 

 the fruit might have later dehisced. 



