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A B S T R A C T Pollen of seven species in 7'etraplasandra and three species in related genera were studied with light and scanning electron microscopes. A new thin-section technique was employed for the study of exine stratification and apertural structure. This study reveals several previously undescribed pollen structures for the group. Trends toward increase in pollen size and in specialization of other pollen characters are evident in Tetraplasandra. Pollen of Reynoldsia and Peekeliopanax differs from Tetraplasandra in the pertectate sexine and the absence of inner nexinous breaks, respectively. A pollen correlation study shows that Munroidendron falls readily within the genus Tetraplasandra but is distinguishable from the latter by its bifurcate colpi. MUCH OF RECENT research of the Araliaceae has been concerned with the floral anatomy, morphology, and taxonomy of the family (Graham, 1966; Smith and Stone, 1968; Eyde and Tseng, 1969 and in press; Philipson, in press); pollen morphology, however, remains to be examined. The present study is parallel to a family-wide investigation of floral evolution in the Araliaceae (Evde and Tseng, in press). i\JIy preliminary survey of pollen in over 50 araliaceous species has shown that pollen data are valuable in generic delimitation and are of evolutionary significance. Attracted by the wide range of flo-al characters (Sherff, 1955; Eyde and Tseng, 1969 and in press) and fruit sizes (Sherff, 1955; Carlquist, 1966) in Tetraplasandra, I examined the pollen of seven species in this genus as well as one species each in Munroidendron, Reynoldsia, and Peekeliopanax. Although the general pollen morphology of several Hawaiian Araliaceae has been described by Selling (1947), his work, which was solely based on whole mounts of grains, is not detailed enough for the present purpose. In this study, both light and scanning electron microscopes were employed. A thin-section technique (Coil, 1968) was employed for the first time for the study of exine stratification and apertural structure. The study has revealed several previously undescribed pollen structures for this group, and has provided a basis for further research on the palynology of the Araliaceae.

Die Pollenmorphologie der nahe verwandten Gattungen Frangula Mill., Oreoherzogia W. Vent und Rhamnus L. (Rhamnus L. s. l.) wurde mit Hilfe des Licht-und des Elektronenmikroskops untersucht. Der Pollen erweist sich als recht einformig gebaut. Unterschiede in der Substruktur zeigen sich in der Stratifikation — besonders in der Ausbildung der Baculazone — sowie im Oberflachenrelief (Ornamentation). Die Ergebnisse werden im Hinblick auf die verwandtschaftlichen Beziehungen der Gattungen diskutiert. The pollen morphology of the closely related genera Frangula Mill., Oreoherzogia W. Vent and Rhamnus L. (Rhamnus L. s. l.) was examined by means of photon and electron microscopy and was found to be rather uniform. Differences in fine structure were observed in exine stratification, especially in the bacula layer, and in ornamentation. The results were discussed with regard to the relationships of the genera.

Pollen exines may be observed directly with the electron microscope following treatment with 2–3 N hydroxide for 2–20 h. The resulting information is easily interpreted and certain details of exine stratification, pore-membrane structure, and channels through the exine wall are apparent that could otherwise be obtained only by elaborate reconstructions from serial thin-sections. Also, a fast and simple method of making single-stage surface replicas is described in which the pollen walls are dissolved with hot 2-aminoethanol and washed with hot distilled water.

A B S T R A C T The pollen wall of Canna generalis Bailey is exceptionally thick, but only a minor part of it contains detectable amounts of sporopollenin. The sporopollenin is in isolated spinules at the exine surface and in the intine near the plasma membrane. There is no sporopollenin in the > 10 ,u thick channeled region between spinules and intine. We suggest that the entire pollen wall of C. generalis is similar to the thick intine and thin exine typical for germinal apertures in many pollen grain types. Considered functionally, the Canna pollen wall may offer an infinite number of sites for pollen tube initiation and would differ significantly from grains that are inaperturate in the sense of an exine lacking definite germinal apertures. THE CANNACEAE are represented by a single genus, Canna, and approximately 50 species. The extensive use of Canna as an ornamental has resulted in numerous hybrids. In a pollen morphological investigation of 48 horticultural varieties of C. indica significant differences were noted in wall ornamentation, sterility, and size (Nair, 1960). The exine stratification patterns, however, have been difficult to interpret as Erdtman (1952) suggested. Sporopollenin as part of an exine is recognized only in spinules at the pollen wall surface but staining of Canna microspores with osmium indicated that there were inclusions within the intine and in the tryphine on the wall surface which looked like sporopollenin. To substantiate the presence of sporopollenin in the above nonexinous locations we followed the disintegration of Canna pollen caused by the acetolysis method of Erdtman (1960). It became evident that the entire wall was similar to the greatly thickened intine and thin exine common to the germinal apertures of many pollen grains. We have drawn upon original electron micrographs of Centrolepis aristata (R. Br.) Roem. and Schultz. and Macrozamia reidlei (Gaud.) C. A. Gardn. to amplify the latter aspect of our results.

Foi estudada a morfologia polínica de sete espécies de palmeiras que ocorrem na floresta subtropical latifoliada do Brasil meridional, dando-se especial ênfase à estratificação das exinas em relação ao aspecto da superfície. A presença de nexina 1 no gênero Butia e a falta desta camada nos deamis gêneros estudados, está de acôrdo com as grandes divisões toxonômicas destas família, bem como a ocorrência ecológica das espécies. The pollinic morphology of seven palm-tree species which occur in the subtropical ombrophilous forest in southern Brazil have been examined. Emphasis have been put in the study of the exine stratification in relation to the superficial aspect of the pollen. The presence of nexine 1 in Butia and the lack of this layer in the other genera, agrees with the taxonomic sub-division of the family, as well as with the ecological distribution of the species here studied.

Pollen tetrads in Typha latifolia result from the fusion of the outermost portion of the exine (the tectum) where microspores within the meiotic tetrad are contiguous. Exine stratification is discussed.

Five fossil pollen forms from Tertiary assemblages in southern New South Wales are shown to have botanical affinities with taxa in the family Euphorbiaceae. Careful comparison of all morphological features of fossil and extant reference pollen, and consideration of as many closely related taxa as possible has enabled these identifications to be made with confidence. The fossil pollen forms Tricolporopollenites endobalteus and Triorites introlirnbatus match the extant Macaranga-Mallotus, and possibly other related taxa. The fossil Polyorificites oblatus is identified with the extant Longetia pollen type, i.e. Austrobuxus (Longetia) buxoides and Dissiliaria tricornis. Most of the specimens of the fossil Malvacipollis divevsus fit the extant Tetracoccus pollen type, ie. Austrobuxus (Longetia) swainii and Dissiliaria baloghioides, and only a very few have malvaceous affinities. An analysis of the exine stratification and the base of the spine is a reliable way of distinguishing spiny pollen of the Euphorbiaceae from that of the Malvaceae. The presence of Micrantheurn-Neoroepera and Alchornea (Caelobogyne) is also established in the fossil record. Only one of the fossil taxa, Micrantheum-Neoroepeva, has living representatives in the temperate zone of Australia today, and the fossil occurs in Upper Tertiary assemblages which usually lack Nothofagus. The other four are Lower Tertiary taxa, found always in assemblages with abundant Nothofagus, and their living representatives are almost entirely restricted to the tropical phytogeographic zone of Australia. This distribution contrasts strongly with the fossil localities in southern New South Wales. Only the Alchornea fossil is a Tertiary tropical element.

Three species of Compositae-Heliantheae have a uniquely complex lamellated structure in the foot layer of the ektexine, as revealed by electron microscopy. The possible importance of this is pointed out. Pollen exine morphology has been found to be constant for a given species and even throughout certain genera; within and among the higher taxonomic categories patterns of variations in exine morphology occur, and are useful in suggesting taxonomic and phylogenetic relationships as well as in distinguishing among unrelated groups (Carlquist, 1961, 1964; Raj, 1961). To date the characters used for taxonomic purposes have been primarily those dealing with exine size, shape, ornamentation, and aperture characteristics. However, Faegri (1956) and Erdtman (1960a, 1960b) have demonstrated with light microscopy that exine stratification based upon morphological and chemical differences exists and can be of systematic importance; they have established two competing terminological systems for designating exine strata. The system developed by Faegri which recognizes the outer, sculptured and basicfuchsin-staining layer as the ektexine and the inner, non-basicfuchsin-staining layer as the endexine has proven to be the most useful in our electron microscopic studies in that chemical staining properties have been found to be equated with morphological organization (Larson and Lewis, 1961; Larson et al., 1962; Skvarla, 1965). The ektexine, as we recognize it (following Faegri and Iversen, 1964), is subdivided into three morphological units: a basally positioned foot layer supporting columellae which in turn support a tectum (Fig. 1) [it is also recognized that any of the three ektexine units may be absent from particular exines]. With the increased resolution provided by electron microscopy these specific units have come under more comprehensive investigation. Of particular significance are the observations made on the foot layer. While the foot layer was shown to be variable in thickness among plant taxa, and even absent in some species (Larson et al., 1962) it was found to be consistently homogeneous in detailed structure and spatially distinct from the under1 This work is part of a Ph.D. dissertation completed at The University of Texas.