1960] 



ANATOMY OF GTJAYANA XYRIDACEAE 



111 



The outermost layer of the pollen grain wall, or sexine, is basically a thin 

 membranous layer which may be partly detached in damaged grains. Minute 

 pila (seen in surface view, figs. 113, 129) are embedded in this membrane. A 

 feature that seems quite important to the writer does not seem to have been 

 mentioned in the literature on Xyridaceae pollen grains, namely, that these 

 minute pila are, in fact, homologous with the large spines or knob-like ornaments 

 in Abolboda and Orectanthe. These larger excrescences are deposited on the 

 membranous layer just as the pila are, and appear to be composed of the same 

 material, despite the vast difference in size between the two types of ornamenta- 

 tion on the same grain. Rarely, as in Orcein nth e sceptrum (fig. 125), knobs 

 transitional in size between these two categories may be observed. The pila in 

 Orectanthe are noticeably larger than those in Abolboda. Pollen grains of 

 Achlyphila (figs. 128, 129) show the largest pila of any of the grains studied 

 here. In Achlyphila, the pila tend to be aggregated in flake-like patches. In 

 places between these patches, the pilate layer is absent. In Abolboda, a thin 

 hyaline layer was observed immediately beneath the pilate layer. Such a layer 

 may also occur in pollen grains of Orectanthe and Achlyphila. 



The spines on pollen grains of Abolboda are so characteristic of that genus, 

 and are so subject to distinctive variations in the species, that they have been 

 figured for all the species studied (figs. 106-120). Basically, as in A. acaulis or 

 A. linearifolia, they have an inverted funnelform shape. Sodium hydroxide 

 treatment (figs. 112, 120) reveals that lacunae, not visible in other preparations,, 

 are probably present in the spine base. Some species show markedly narrow 

 spines: A. bclla (fig. 108), A. acieularis (fig. 107), and A. ciliata (fig. 109). 

 Very short, wide spines occur in A. ebracteata (fig. 110) and A. macrostachya 

 var. robustior (fig. 120). The three varieties of A. macrostachya appear different 

 on the basis of spine size and shape. Within a single flower of A. sprucei, 

 various alterations in spine shape were noted. The basic condition seems to be 

 that shown in figure 114, but multiple spines on a single base (fig. 115), very 

 much reduced lobes (fig. 116), and merely the vestige of the spine-base (fig. 117) 

 Avere also observed. 



Erdtman (1952) has illustrated the spines of pollen grains of three species 

 and given dimensions:^, poarchon (spines 8.3 p long; basal diameter 5.5 /*), 

 A. pulchella (spines 9.3 p long; basal diameter 8.3 p), and A. vaginata (spines 

 8.3 fi long; basal diameter 8 p). Erdtman figures spines in the latter species 

 which appear about like the spines in A. macrostachya var. angustior. 



The comparable ornamentation on pollen grains of Orectanthe is generically 

 different from that of Abolboda. In Orectanthe, the emergences take the form of 

 a large knob, or other shape much wider and more blunt than the spines of 

 Abolboda, with the possible exception of the much smaller structures in A. 

 sprucei. In O. ptaritepuiana (figs. 121-124) a variety of shapes was noted, 

 varying with the collection from which the grain was taken : short, with a 

 rounded apex (fig. 121), elongate (fig. 122), with a curved apex (fig. 123), or 

 with folds or bulges on the sides (fig. 124). Evidently considerable variation is 



A. ciliata. Fig. 110. A. ebracteata. Fig. 111. A. grandis var. guayanensis. Fig. 112. A. 



linearifolia .(from NaOH-treated specimen). Fig. 113. Same, surface view of interspinal 



sexine ornamentation. Fig. 114. A. sprucei. Fig. 115-117. Same, variations (within a sin- 

 gle flower) or ornament shape. Scale = 5 jx. 



