An exine architecture model for viscin threads

Structure of the exine ofEpilobium angustifolium(Onagraceae)

“…5 and also the outer part of the exine, then there would be solid appearing columellae, about a micrometer in diameter, and a thick and solid tectum. Our findings concerning the rod-like structure of the ectexine of E. arzgzrsfifoliirriz pollen agree with Hesse's (1984) model of the structure of Epilobiiitiz exine and the results of Skvarla et al (1978) and Patel et al (1984) on the attachment of its viscin threads to the exine. There is a similarity between the unit structures described in this report and the rod-like structures of exines of Artetiiisia (Rowley et al 1981); of Befiila (Dunbar & Rowley 1984, Claugher & Rowley 1987; of Epilobiirrii (Rowley 1988); of Fagiis (Claugher & Rowley 1990); Ecliiriops (Blackmore 1990), and Qiicrciis (Rowley and Claugher 1991).…”

“…These authors group Epilobiitiii together with those taxa of the family having pollen without distinct columellae. Hesse (1981Hesse ( , 1984 and Patel et al (1984 e.g, Plate 62, A) showed viscin threads to be continuous with the rod structures of pollen exines (here called exine unit-structures) of onagraceous plants (see Skvarla et al 1978, for structure of viscin threads). Hesse's model suggest further that the tectum and rest of the ectexine is also made up of rods.…”

“…Hesse's model suggest further that the tectum and rest of the ectexine is also made up of rods. The coluinellae appear in Hesse's (1984) model, in very schematic form, as the fused bases of the rods making up the rest of the ectexine. Rowley's interpretation (Rowley 1983(Rowley , 1995 based on transmission electron micrographs (TEMs) is that the rod structures (exine units) are composed of a core surrounded by binder subunits.…”

Freeze Fracture and Cytoplasmic Maceration of Pollen Grains

“…From the findings of Skvarla et al (1978) this is presumed to be the proximal hemisphere. Skvarla et al (1978) and subsequent workers (Hesse 1981(Hesse , 1984) have described the banded or segmented appearance typical of viscin threads in many Onagraceae, this w a s visible at higher magnifications (Fig. 8).…”

Notes on the exine ultrastructure of Onagraceae and Rhododendroideae (Ericaceae)

“…In a11 probability there is a connection between the development of the cxine and that of the viscin threads. The assumption by Hesse (1984) that the manifold thread configurations may be attributed to a single exine arcbitecture principle seems to be correct. He deduces his model on the cxistance of columcllae, there arc however no typical columcllae 'in the investigated species of the Onagraceae and the Rhododendroideae.…”