1960] 



ANATOMY OF GUAYANA XYRIDACEAE 



105 



The innermost layer (fig. 97) consists of more or less isodiametric cells, with 

 contents as noted above. Cell layers internal to this layer (i.e., nncellar layers) 

 are completely collapsed at maturity, and only a thin membrane of collapsed 

 cell walls separates the endosperm from the innermost layer just mentioned. 

 At the chalazal end of the ovule (fig. 98), the structure is altered. Instead of 

 the four distinctive layers, numerous layers are present. These consist of cells 

 like those of the innermost seed coat layer, with the same dense contents. They 

 form a sort of operculum in the seed. In immature seeds, a number of nucellar 

 layers which might be mistaken for a haustorium are present; during matura- 

 tion stages, these collapse. The way in which the two layers with contents are 

 altered at the micropyle is indicated in figure 101. The lumen of these cells is 

 quite small in comparison with the thickness of the wall, and a two-layered wall 

 condition is visible in the outer row of cells. Mention should be made of the fact 

 that during maturation of the seed, walls of the cells with contents are obliter- 

 ated, so that limits between these cells may be difficult to ascertain. 



Orectanthe. 



The single section shown (fig. 103) will serve to indicate the nature of the 

 seed coat in this genus. The number of layers outside of the inner two may be 

 greater or fewer than that shown, but is never fewer than three cell layers and 

 usually more, depending on ring formation. The outermost layer of cells con- 

 sists of thin-walled sclereids. A number of thin-walled but persistent cells 

 are present between the epidermis and the inner pair of cell layers. The 

 persistent tissue is distinctive only in the presence of intercellular deposits, 

 which occur in irregular patches and are of the same material which fills lumina 

 of the innermost pair of cell layers of the seed coat. The inner two cell layers 

 are distinctive, as in Aboil) odd, in their occlusion with the resin-like or tannin- 

 like contents. In origin and nature, these cell layers are precisely homologous 

 with those two layers in Abolboda. The outer of these layers does not exhibit 

 the remarkable alteration into ridges which occurs in Abolboda, however. 



Comparison of Seed Coats in Xyridaceae. 



Unfortunately, no seeds of Achlyphila distich a were available. There are 

 descriptions of seeds of Xyris in the literature, although only for one species, 

 A', indica (Weinzieher 1913; Netolitzky 1926). These descriptions show a layer 

 of cells with dark contents, formed into longitudinal ridges on the seeds, which 

 has sculpturing on the outer wall surface and appears to correspond with the 

 similar layers with contents in Abolboda and Orectanthe. AYeinzieher, however, 

 suggests that the origin of this layer is from the inner layer of the outer integu- 

 ment, rather than the outer layer of the inner integument, as is the case in 

 Abolboda. Careful comparative studies of ovules in Abolboda and Orectanthe 



taken between longitudinal ridges. Fig. 100. Transection of seed coat, showing two ridges 

 in sectional view. Figures 94-97 represent successive levels of the seed coat from outside 

 to inside. They can best be understood by visualizing them as four levels, from top to bottom 

 in succession, of the portion shown in figure 100. Fig. 94. Epidermis of seed coat ; outline of 

 ridge shown in broken lines. Fig. 95. Hypodermal level, showing two of the longitudinal 

 ridges. Fig. 96. Subhypodermal layer, showing tannin-filled cells of ' ' valley ' ' between two 

 ridges. Fig. 97. Innermost tannin-filled layer. Figures 98-100 show the cell types mentioned. 

 Note thick wall with ridged surface in subhypodermal layer. Scale = 0.2 mm in 0.1 mm 

 divisions. 



