﻿OVULATE CONES. I I 7 



number of these layers varying with the fruit and the species. Aside from the 

 usually regular distribution described, the scales may be unequally distributed in 

 patches, or on certain sides of a fruit there may be outside the outermost pedicels 

 large areas made up exclusively of small and densely packed scales, sometimes 

 amounting to a third or even a half of the bulk of the enti'e fruit. (See fig. 58 

 and plate xxvi.) Likewise certain smaller pedicel structures must be abortive, and 

 must fail to develop seeds, although much advanced beyond the reduced condition 

 of the scales. The outer and thus more basally borne scales are of shorter and 

 shorter length. At the point of their insertion the scales are thin and filamentous, 

 but they slowly increase in thickness to the region of the seeds, where they are on 

 any or all sides scooped out so as to form the cavities in which the seeds lie closely 

 enveloped. Beyond the seeds the scales again expand into the more or less regu- 

 larly prismatic tips so closely surrounding the micropylar tubes and thus giving to 

 the surface of the fruit the characteristic pattern already noted and shown in figures 

 55 and 57. Beneath the lowermost of the seeds the ends of the interseminal scales 

 assume a more regular tetragonal to hexagonal form, regularly decreasing in size 

 to the sterile basal region of the cone. It is a surface view of the cone base, show- 

 ing the pattern formed by the ends of the interseminal scales which Seward has 

 figured in the Jurassic Flora of Yorkshire (149, text-figure 35), as the "surface view 

 of the base of a flower" of Williamsonia pecten (Phill.). The form of the seed 

 stems with the apically-borne seed and of the adjacent interseminal scales is clearly 

 outlined in all the accompanying figures of longitudinal sections. In all transverse 

 sections of entire cones the interseminal scales appear to vary greatly in size because 

 cut at a constantly varying height, the larger sections being mostly from centrally- 

 borne scales, and the smaller and flatter mostly from peripherally-inserted scales. 



Histology. — As shown in figure 61 b, in all the middle portions of the fruit 

 beneath the seed layer, in those rarer instances where preservation is so wonderfully 

 complete, as in most of the ovulate strobili of cycad 393, the transverse section 

 shows the interseminal scale to consist in (1) a central group of elongate lignified 

 cells that may be considered a typical bundle xylem ; (2) phloem cells 011 the 

 edges of the central xylem not always forming well-marked areas of cells, but some- 

 times more prominent, depending on the altitude at which the scale is cut ; (3) large- 

 celled elements surrounding the central bundle region similarly to those of the 

 heavy outer woody zone of the seed stems, but with thinner walls than in the latter ; 

 (4) heavy cortical cells; (5) the outer layer of the interseminal scale, composed of 

 small, elongate, heavy-walled cells one cell thick. The true nature of this layer is 

 not at first apparent. Wherever the interseminal scales abut on the seed pedicels 

 there is what appears to be a very characteristic layer of small outer epidermal 

 cells, forming a common boundary between these two organs (cf. fig. 60 c and 

 photograph 2, plate xxvn). That this epidermal sheath forms the true outer layer 

 of the interseminal scales, although a structural arrangement hitherto overlooked, is, 

 however, very clear, because of the fact that it is double wherever two of these scales 

 abut on each other, and always single between a scale and an adjacent seed pedicel. 



In such sections as 393 {cf plate xxvi), 394, also 3, 7, and 220, preservation is 

 confined to lignified elements, and the arrangement of scale boundaries just described 



