XXXVI] CYCADEOIDEA 393 



sporophylls. The rounded surface of the receptacle is covered 

 with a dense cluster of long slender appendages, seed-stalks and 

 interseminal scales, the latter being much more numerous than 

 the former (fig. 521, A, B). These organs are believed to be homo- 

 logous foliar structures, the seed-stalks being megasporophylls 

 and the interseminal scales abortive or potential sporophylls 

 (see also figs. 562, 563). Fig. 514 shows the form of a single flower 

 from an American stem closely allied to Cycadeoidea Gibsoniana. 



FIG. 522. Cycadeoidea Gibsoniana. Longitudinal section of flower showing half 

 the receptacle with part of the absciss-layer, a. (British Museum.) 



The megasporophylls are more or less polygonal in transverse 

 section : there is a central concentric vascular strand surrounded 

 by a thick cortex (fig. 527) : at its upper end the sporophyll 

 bears a single orthotropous seed containing a dicotyledonous 

 embryo (figs. 521, D, E ; 523). The vascular strand pierces the 

 base of the testa and expands to form a shallow cup of tracheal 

 tissue in the chalaza ; there are no bundles in the single integument. 

 The testa (fig. 521, D, t) consists of three regions, a median layer 

 of rather large rectangular or palisade-cells with an inner and outer 

 tissue composed of much smaller cells. The testa is prolonged 



