SUMMARYElectron microscopy reveals that the multicellular hairs, in the Anabaena-cont&ining leaf cavities of Azolla, produce labyrinthine wall ingrowths, and have dense cytoplasm with numerous mitochondria and abundant endoplasmic reticulum. Development of transfer cell morphology, in this location, might be an adaptation facilitating interchange of metabolites between Azolla and its algal partner. Equally prominent wall ingrowths are also found in the absence of Anabaena. It is suggested that they may be either a constitutive feature of Azolla or may be induced as a response to the presence of combined nitrogen sources in the axenic culture medium. The occurrence of plasmalemmasomes, in the developing hair-cells of Azolla, is compared with their presence in lichens, mycorrhiza and at host-parasite interfaces.

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A scanning electron microscope fitted with a sensitive cathodoluminescence detector system has been used for the identification of pollen grains stained with acridine orange or unstained. This approach provides a means of identifying and studying the morphological details of pollens. Cathodoluminescence detection can, in principle, extend the limits of resolution beyond those obtainable with the fluorescence microscope.Fluorescence microscopy techniques using acridine orange have proved useful in the identification of pollens, (Ratclqfe and Griggs 1963, Shellhorn and Hull 1964), but their detailed morphological structure cannot be studied in the light microscope.Scanning electron microscopy (SEM) has been extensively used in studying the morphological details of pollen grains. The scanning electron microscope (SEM) can be fitted with a cathodoluminescence (CL) detector system and recent improvements in light collection by these systems (Herbst and Hoder 1978), have allowed the identification of herbicides (Falk 1974), and location of the fluorescein labeled anti-IgG-induced caps on mouse lymphocytes (Soni et al. 1975), fungal spores (Tuenia) in a human hair (Muir et al. 1971), unstained hyphae and spores of a fungus which causes pityriasis versicolor in human skin (Mulassezia furfur) (Curreuud et al. 1972). This approach has been little explored in the identification of pollens.In the present study, I examined the pollens of Red cedar (Juniperus virginiana) , Red maple (Acer rubrum) , Corn (Zea mays) and Yellow dock (Rumex crispw) in a Stereoscan Cambridge Mark I1 fitted with a sensitive CL detector system (Bond et al. 1974). The materials were obtained from the Herbarium of Canada Department of Agriculture, Ottawa.The pollens (stained with acridine orange or unstained) were directly mounted on the stubs with Aquadag and examined in SEM. The SEM was oper-ated at 20 kV with a beam current of 150pA. The uncoated pollens were examined in the secondary electron mode (Figs. 1,3,5,7) and CL mode (Figs. 2,4,6, 8). Polaroid film (type 42) was used at exposure times of 40 s for both modes. For some species the unstained pollen gave a more intense CL signal (Figs. 2,6,8) and for other species the signal was enhanced by staining ( Fig. 4).After the uncoated pollens had been examined in the secondary electron mode and for CL, the same pollens could then be coated with gold and examined again in the secondary electron mode to study their morphological details. Since gold coating tends to absorb emitted light, the best CL micrographs were obtained on the uncoated samples. The images obtained by CL could be compared with secondary electron micrographs taken on the same pollens before and after coating with gold. This technique provides a means of identifying and also studying the morphological details of the pollens in the SEM and can, in principle, extend the limits of resolution beyond those obtainable with the fluorescence microscope. ReferencesRatcliffe H E, Griggs W H: The identification of pollen grains using fluoresc...

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