﻿272 AMERICAN FOSSIL CYCADS. 



difference exhibited by the Calvados seeds consists in the thickening of the integument in 

 the apical region, as shared in by both the palisade and underlying fleshy hypodermal layer. 

 These are clearly outlined in the figure as an outer light-colored and an inner dark-colored 

 zone enveloping the nucellus. 



Photomicrograph 4. — C. excelsa (T. 481). S. 183. X 20. Somewhat oblique section 

 through summit of seeds and enveloping interseminal scales. These seeds are rather younger 

 than those of the Calvados specimen shown in the preceding section. In the original sec- 

 tion itself the thick-walled cells composing the expanded tips of the interseminal scales are 

 seen to be remarkably well preserved, and to exhibit scalariform markings very similar to 

 those of the bracts surrounding the strobili. 



Photograph 5. — C. colossalis (T. 354). S. 128. X 10. Transverse section through a 

 very young ovulate cone in which the seed pedicels have not yet elongated. The pedicels of 

 this species (as well as the very similar C. dacotensis, minnekahtensis, etc.), do not, how- 

 ever, attain at any time as great length as in the other species illustrated on this plate. (An 

 hypogynous and dehiscent disk may have been present.) 



Photograph 6. — Cycadeoidea turrita. X 4- Transverse section of ovulate strobilus 

 traversing lowermost seeds. 



Photomicrograph 7. — Cycadeoidea Wiclandi (T. 77). S. 102. X 16. A transverse 

 section that was cut obliquely through the summit of the parenchymatous receptacle of an 

 ovulate cone to show the insertion of the seed pedicels and surrounding interseminal scales. 

 The central bundle of the pedicels is seated highest on the large and pithy cells beneath, the 

 imall-celled cortical region next lowest, and the interseminal scales lowest of all, whence 

 the latter project brush-like beyond the end of the cortical zone in longitudinal sections, as 

 may be seen in photographs 1 and 2 of the succeeding plate xxix. This explains how in all 

 the upper portion of the present photograph the section passes beneath the basal tissue of 

 the pedicels, although the latter are clearly outlined by the system of enveloping interseminal 

 scales. The relations described were found difficult to photograph, although clearly defined 

 in the original section 102. 



Plate XXIX. Peculiarities of Cycadeoidean Fruit Silicification, as 

 shown by Photomicrographs. 



1. Basal region of seed pedicels and interseminal scales finely conserved, with the result 

 that differentiation of separate organs is not distinct as in the succeeding photomicrograph 

 of similar but less perfectly conserved organs. T. 77. S. 2. 



2. Basal region of seed pedicels and interseminal scales preserved with vague outlining 

 of individual cells, but otherwise clear demarcation of organs. At the top of the photomi- 

 crograph the several pedicels are lettered in succession {a, b, c, d, e), and the number of the 

 intervening scales is also indicated by accents (')• As in the preceding instance the woody 

 mass of stems and scales has split away from the pithy tissue of the receptacle. The trans- 

 verse section through another cone, photograph 7, plate xxvm, supplements these illus- 

 trations. 



3. Interseminal scales and pedicels from near seed zone. Only partially preserved and 

 traversed by numerous pheno- or sphaerocrysts. T. 77. X 16. 



4. A type of "parenchymatous-cushion," or receptacle preservation, frequently noted. 

 Individual cells of the parenchyma sometimes present, but mostly indistinct, with numerous 

 sphaerocrysts, varying from minute forms to about the size of a parenchyma cell, the whole 

 being traversed by numerous gum ducts or elongated secretory sacs. T. 66 (C. turrita). 

 S. 29. X 16. 



5 and 6. The usual type of seed preservation, with the tissues of the integument more 

 or less distinct and the interior cavity filled with clear silica, often containing large pheno- 

 or sphxrocrysts. Note that in No. 6 the decrease of the cortical region of the pedicel at 

 the seed base is very clearly shown in the case of the middle seed. Photomicrograph 5 

 from T. 77 (S. 7. X 20). Photograph 6 from T. 15 (S. 89. X 20). 



