386 G. R. Wieland — American Fossil Cyeads. 



Seed Stems. — These are very closely set on the cushion, and 

 as it is difficult to separate their elements from those of the 

 interseminal scales in the longitudinal sections, they may be 

 best studied in transverse sections. Such a section from the 

 middle of the fruit is shown in figures 14 and 16, Plate X, 

 where the stem is seen to consist of a central vascular bundle 

 enclosed in an endodermis which is surrounded by a broad 

 woody outer layer, or xylem zone, the " enveloppe tubuleuse " 

 of Lignier. 



Each seed stem is uniformly surrounded by from 5 to 6 

 interseminal scales. A series of transverse sections from the 

 base to the summit shows no variation from this general 

 arrangement, although there is a slow diminution in the 

 diameter of the stems, accompanied by marked changes in the 

 cell conformation of the xylem zone. In this and other 

 species, there is often at the base a strong compression of 

 the surrounding scales, while the xylem areas are more 

 or less polygonal and composed of cells quite regularly sub- 

 rhombic in section. Of these, from 30 to 40 may be counted 

 radially, as shown in figure 4, Plate VIII. Towards the 

 summit there is a constant increase in the size and regularity 

 of these cells, which finally become quite round, accompanied 

 by a decrease in the width of the xylem band, until at the 

 base of the seeds it consists of but two layers of cells surround- 

 ing the central bundle, which remains constant in character. 



This bundle is well illustrated in the enlarged view given in 

 figure 15, Plate X. Centrally there are from 3 to 10 small 

 woody elements. These are enveloped in soft parenchyma, 

 not preserved in all specimens, and the bundle terminates in a 

 well-marked endodermis. Such concentric bundles recall the 

 somewhat similar structures seen in many ferns. The 

 atrophied peduncles, or those lacking a well-marked central 

 bundle, described by Lignier in C. (Bennettites) Morierie, have 

 not been observed thus far. The interesting case of bifid 

 seed stems, or those with two central bundles within the same 

 tubular, or xylem zone, however, rarely repeats itself in the 

 present specimens. 



It may be mentioned that while the figure of the transverse 

 section of the seed stems, " vascular cords," given by Car- 

 ruthers is a faithful one, its being cut too near the base, where 

 there is much compression of the several elements, prevented a 

 true conception of their significance. Only at some distance 

 above the base does the clear differentiation of parts seen in 

 figure 14, Plate X, appear. Judging from the transverse 

 section by Carruthers, just mentioned, and the additional one 

 given by Solms-Lanbach, the tubular layer, or xylem zone, of 

 G. (Bennettites) Gibsonianus was composed of more angular 

 cells than in the case of the present specimen. 



