﻿120 REPRODUCTIVE STRUCTURES. 



group of small xylem cells, followed by a wide area of enveloping phloem, with a sur- 

 rounding bundle sheath composed of very regularly disposed cells of slightly less 

 diameter than those of the succeeding cortex, as shown in the various photographs 

 of transverse sections of fruits from trunk 393. Aside from the presence of a sheath, 

 the central bundle very nearly agrees in structure with that of the interseminal scales. 



The relations between the pedicels and scales clearly appear in figure 6 1 , together 

 with the fact that serial sections throughout all the upper portion of both sets of 

 organs are afforded by one and the same transverse section of the cone, if cut at or 

 just beneath the lowermost seeds. Thus in subfigure A of figure 61 the seed pedicel, 

 as cut near its middle region several centimeters beneath the apical seed it bears, 

 has a broad cortex ten or a dozen cells thick ; while the more distally cut pedicel 

 in subfigure c, from the periphery of the same transverse cone section, is seen about 

 5 mm. beneath termination in the seed base, and has a cortical thickness of from 

 three to six cells. Finally, there is to be noted in the area at the lower right-hand 

 corner of c, which lies nearest the periphery of the cone, a pedicel cut at its most 

 constricted point beneath the seed base, where the pedicel cortex is but two or three 

 cells thick. As explained more fully below, these few remaining cortical cells con- 

 tinue on above the seed base and thin out, as a sort of cup-like seed support. 

 Conversely, comparison of the subfigures B and c of figure 6 1 shows the correspond- 

 ing increase in size and degree of lignification of the scales. 



The main difference between the stem region of the fertile and the sterile or 

 scale series plainly consists in the fact that the former have lost their epidermal 

 ensheathing layer and the latter the bundle sheath and most of the cortex. Aside 

 from this balanced form of reduction, as it were, the stem organization of both 

 appears to be fundamentally the same. In so far as such a comparison may be made 

 to express anything, the structure of the scales is much more like that of the pedicels 

 than is the structure of the enveloping bracts like that of foliage leaf bases. It is, 

 above all things, possible that related forms have existed in which the organs repre- 

 sented by the scales, though perhaps present in much fewer number, were all fertile. 

 Moreover, the extensive reduction of both scales and pedicels is conclusively indi- 

 cated by the occurrence of the plural bundles in the basal interseminal scales of 

 Bennettitcs Morierei (86«). 



SEEDS. 



The fertile pedicels bear a single orthotropous seed, the size of a small grain of 

 rye. The xylem of the central vascular bundle of the pedicel ends in a salver-like 

 chalazal region made up of scalariform cells, the outer of which continue into the 

 thin nucellar wall. The exterior phloem and the enveloping bundle sheath severally 

 give rise to the double-layered integument. The wide outer cortex, instead of 

 passing over into an outer integumentary layer, forms a cup-shaped supporting basal 

 husk which rapidly thins out along the sides of the seed as its diameter increases 

 until in the middle region only a few tubular cells may be left lying as loose ends 

 on the true outer surface of the seed, as formed by the transition of bundle-sheath 

 cells into the squarish or polygonal forms shown in the drawing (fig. 62). The 

 seeds in the sections before us, as cut from a number of different fruits borne by 

 cycad 393, are supposed to approach the mature size and are, exclusive of the 



