Il8 CORDAITEAE. 



Gnetaceae or to some other groups of Gymnosperms not yet sufficiently 

 recognised and defined. But since it is not possible at present to distinguish 

 these remains according to their origin, we must be content here with some 

 general remarks upon the whole group. 



All the seeds studied by Brongniart were formed from orthotropous 

 ovules, and, as has been already said, are of essentially the same structure, 

 whatever difference there may be in details. They are inclosed in a well- 

 preserved and often very thick testa, which is in some cases homogeneous 

 and lignified, but in many others has an outer fleshily succulent layer like 

 that in the seeds of Ginkgo. The happily chosen terms sarcotesta and 

 cndotesta have been applied to the two layers. Where the testa appears to 

 be formed of one layer only, it is not indeed always certain that there was 

 not originally a sarcotesta which was destroyed before petrifaction ; even in 

 the casts known as Rhabdocarpus traces of impressions have occasionally 

 been seen, which suggest the former existence of such a layer 1 . From ripe 

 seeds not well preserved in all their parts it is obvious that we cannot 

 always be sure of the number of the integuments in the ovule. The nucellus 

 lies in almost all cases immediately inside the testa ; Pachytesta, Brongn., 

 is the only species in which the apex of the nucellus is enveloped in a 

 distinctly discernible innermost integument 2 . In other forms such differ- 

 entiations, though they may possibly have been in existence at the period 

 of flowering, can no longer be perceived. In many cases the nucellus is 

 quite destroyed, or its outer boundary only is preserved in the form of a 

 fine line ; in its place there is usually a cavity, the wall of which is lined 

 with crystals of quartz. In the best state of preservation the tissue of the 

 nucellus has disappeared up to the outermost boundary line, but the embryo- 

 sac with the endosperm inclosed in it is plainly seen. The egg-cells appear 

 in the convexity of the upper end of the endosperm, separated by some 

 distance from each other, as is usual in Cycadeae, and generally distinguished 

 by their shrunken brown contents. Cardiocarpus sclerotesta, C. augustodu- 

 nensis and Taxospermum Gruneri supply good examples of these phenomena 

 (Fig. 10). The structure of the apex of the nucellus is highly characteristic 

 in all the forms ; its tissue seems to have possessed greater power of 

 resistance, and is seen usually in a good state of preservation on the top of 

 the bounding line which indicates the nucellus. It forms a conical projection, 

 and is pierced by a canal which widens below into a pollen-chamber in some 

 cases (Stephanospermum akenioides, Fig. 10, A c] of considerable dimensions, 

 and usually containing numerous pollen-grains. The structure agrees 

 thoroughly in all these points with that of the female flowers of Cordaiteae 

 described above. The course of the vascular bundle in the seeds follows 

 closely that which is customary in Cycadeae. The single bundle ter- 



Schmitz (1). a Brongniart 6 , tt. 18, 19. 



