﻿124 REPRODUCTIVE STRUCTURES. 



sided forms, with heavy walls on the embryo side. Interior to this layer is a thin 

 tissue (g), unfortunately quite without exception indistinctly preserved, but seem- 

 ingly made up of elongate to stringy elements, only a cell or two thick. The 

 structure of the seed coat of C. Wielandi Ward is hence quite exactly comparable to 

 that of Lagenostoma, and it appears that {cf. section 108, plate xxviii, photograph i) 

 the palisaded layer (b) of Benncttites Morierei, of the Oxfordian Jurassic, has been 

 eliminated, the integumentary variations from the latter in such case being of 

 generic rather than specific value. On the other hand, Bennettites Gibsonianus 

 is an intervening form which more nearly resembles B. Morierei, the layer (/;) of 

 the latter being represented by oblong cells not palisaded. 



It remains to add that of all forms existing and extinct thus far discovered the 

 most striking structural parallel to the American Cycadeoidea seeds is afforded by 

 Lagenostoma. In both these genera the seeds are incased in an outer palisaded 

 layer, the entire integuments being strikingly similar in organization, barring the 

 fact that in the far more primitive seed Lagenostoma there is an apical complica- 

 tion of the integument forming a hollow fluted dome about the pollen chamber. 

 This is, however, plainly explicable as a vestigial structure ; for integumental folds, 

 chambers, flutings, or other attachments would be more evident in the primitive 

 seeds of the Paleozoic than in the later forms on the hypothesis of Engler, now so 

 fully sustained by paleoutologic evidence, that all cycad seeds are in reality single 

 giant spores inclosed in an integument derived from an indusium and a synangial 

 wall of Marattiaceous type. As the Cycadeoidea seeds are of such pronounced radial 

 symmetry and many times smaller than those of Lagenostoma, comparable in size 

 to a small hazel nut, it is scarcely to be expected that a nucellar-bundle ring can be 

 so well marked or pronounced as in the latter form. 



Embryos and Pre-embryonal Structures. 



In both the European species Bennettites Gibsonianus and B. Morierei, and in 

 the American species Cycadeoidea dacotensis and C. Wielandi, the nucellus often con- 

 tains more or less well marked dicotyledonous embryos, which more or less nearly fill 

 its entire space, and indicate a nearly, if not a completely, exalbuminous condition. 

 In size and general form these embryos, as figured by Solms (157) in Bennettites 

 Morierei, and by Scott (135) in B. Gibsonianus, are strikingly like the embryos of 

 Ginkgo biloba, except that in the basal region of the cotyledons of the species Cyca- 

 deoidea Wielandi (trunk 131) small rounded protuberances are present, recalling 

 Encephalartos. The individual cells of the embryo tissue, while not for the greater 

 part very distinct, are often clearly present. 



It is also of extreme interest that in the sections prepared by the writer from 

 cycad 393 there is represented an earlier or pre-embryonic stage which has never 

 been found preserved in any other specimen, or hitherto observed in any other 

 fossil gymnosperm or other plant. In many of the seeds, as seen in the several 

 different cones of trunk 393, the nucellar space is filled with clear quartz, in part 

 crystalline. In others there is a staining present that must have been conditioned 

 by structure, but definite tissues can not be determined. In still others it is of 

 interest to note that the nucellar wall has collapsed and occupies a central posi- 



