Many improvements have been made in the technique of epi-illumination light microscopy. These modifications have resulted in micrographs of better resolution and subsequently in greater flexibility in the study of floral and vegetative apices. The preparation, mounting, microscopy, and photography of apices are discussed in detail. The correlation of this technique with others such as scanning electron microscopy and serial sectioning is discussed. The numerous applications of epi-illumination light microscopy are considered.

SUMMARYTwo lichen species of the genus Umbilicaria were transplanted into each other's habitat in order to determine the role of winter field conditions in regulating distribution patterns. U. vellea (L.) Ach., which normally grows in a steeply inclined, snow free habitat, was transplated into the level-ground, snow-covered habitat of U. deusta (L.) Baum. The opposite was done for U. deusta. Suitable controls to test the effect of transplanting were also run for both species. The reciprocal transplantation was done in each of two years, one of which had a normal snow load, the other which had almost no snow cover.The effect of reciprocal transplantation was to reduce significantly the carbon fixing ability in U. vellea in the year with the normal snow-load. Transplantation had no effect on U. deusta. The effects on COg exchange were only slight for U. vellea in the year with the lesser snow-load. It is therefore concluded that existing winter field conditions, and especially the nature of the snow cover, maintain the existing distribution pattern of the lichens in the field.

The gross morphology and fine structure of tissue layers in five Umbilicaria species (U. vellea, U. mammulata, U. papulosa, U. muhlenbergii, and U. deusta) were examined using bright-field and transmission electron microscopy. Differences in the surface topography of the upper and lower cortexes of the five species were found. Four of the species contained an osmiophilic banding material on the walls of the outermost file of living upper cortical hyphae. Although the fine structure of phycobiont cells was basically similar for all species, U. vellea was found to have smaller amounts of stored starch and peripheral lipid in cells of the algal zone than the other four species. Algal–fungal contacts were not haustorial, although aplanospore clusters were penetrated by wedge-shaped intrusive hyphae. Senescent algal cells accumulated large numbers of starch grains. Hyphae in the medullary zones were found to be similar for all species with the exception of U. muhlenbergii, which had an extrahyphal, gel-like matrix. Extensive, sheetlike lamellae were also present in the lower cortex of this species. It would appear that many aspects of thallus fine structure and morphology have a direct effect on gas exchange and water relations responses previously reported in the literature.

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Results of histochemical tests performed on fresh root tissue of Ranunculus acris provide the following information on the chemical nature of the root endodermis: (i) the Casparian strip is impregnated with lipid and possibly lignin, (ii) the suberin lamellae stain positively for lipid and phenols with free hydroxyl groups, and (iii) the tertiary wall contains alternating bands of lignin and cellulose.At the ultrastructural level, phenolic 'globules' present in vacuoles of adjacent cortical cells increase in size by accretion of flocculent material and the addition of dispersed granular material through the apparent fusion of smaller vacuoles with the large central vacuole. Globules adhering to fragments of the tonoplast membrane are clearly seen with the SEM.The ferric chloride test for catechol-type phenols at the TEM level proved useful in categorizing phenolic compounds present in intercellular spaces, in walls and vacuoles of cortical cells, surrounding starch grains in amyloplasts, and in the cytoplasm of endodermal cells. Prominent plastids containing large deposits of lipid, osmiophilic material, thylakoid membranes, and starch are seen to be a major constituent of cytoplasm in endodermal and cortical cells.