﻿BISPORANGIATE AXES. 



149 



no distinct tendency to preservation of the soft tissues of the receptacular region. 

 While the smaller xylem elements may occur within the main group of xylem 

 cells, they are a little more abundant at the inner angle in the normal proto-xylem 

 position. As the spiral elements are small and all so distinctly marked and 

 unstretched, these bundles may be regarded as young. The structures preserved 

 show well the immature condition of the central cone, and indicate that it could 

 not have been close-fertilized, unless the pollen of the accompanying fronds retained 



Fig. 74. — Cycadeoidea dacotensis. 



Two transverse sections from a bisporangiate strobilus with a quite complete summit, the upper section being cut above the 

 summit of the central cone or relatively higher than section 367. figure 73, and showing the distribution of the microspor- 

 ophylls and their bundle systems with diagrammatic clearness. The lower section, which is nearly intermediate in rela- 

 tive position between sections 365 and 366, figure 73, shows the double row of bundles as seen in the disk base to be 

 breaking up into the separate frond patterns. The exquisitely handsome sections from which these drawings were made 

 belong to the museuim of the State University of Iowa. (See the photographs 1,1a, Plate XXXV.) 



its vitality for months after being shed, as does the pollen of living cycads, assum- 

 ing, of course, that the ovules are not abortive, but simply young, as indicated by 

 comparison of various forms of young fructifications described in the next chapter. 

 The considerable time gap between the maturation of pollen and ovules may have 

 made cross-fertilization the rule in these bisexual flowers. 



THE STAMINATE DISK. 



In all its essential structures the staminate disk is new to science, although in 

 part, as we have already seen, long known in the form of isolated imprints of prob- 

 lematical function — sometimes held to be "carpellary," and sometimes apical and 



