Lakes of south-western Uganda

The vegetation of Lake Bunyonyi, a high altitude lake in Kigezi, S.W. Uganda, is described. The lake had two distinct plant communities. In the shallow sheltered bays and inflows extensive floating swamps of Cyperus papyrus L. and Cladium janiaicen. se Cranz. existed. On the steep, exposed shores there was only a narrow band of vegetation, dominated by firmly rooted Phragmites australis (Cav.) Steud., usually with papyrus behind. Floating-leaved Potamogeton and Nymphaea sometimes occurred outside the emergent species, and submerged species, including Ceratophyllum demersum L. grew down to 8 m. The pattern of vegetation, and the contribution of floating islands to the distribution of plants in the lake is discussed. Susceptibility to fragmentation, and distribution by wind are thought to be major factors governing the pattern. Oxygen proflies measured at the fringe of swamps indicated that the swamps did not cause appreciable deoxygenation of the water.     

Age-Specific Differentiations during the Development of the Rat Submandibular Gland

Histological observations indicate that the rodent submanfibular salivary gland does not complete its development until adulthood. Reports in the literature based upon enzyme studies suggest that the gland may pass through several stages of differentiation from birth to adulthood. Considering that proteases appear late in the developmental sequence and could cause apparent changes in enzyme concentrations, a methodology free of possible protease-mediated artefacts has been developed to analyze the patterns of protein accumulations. Analysis of total trichloroacetic acid-precipitable proteins on acrylamide gradient slab gels with sodium dodecyl sulphate and urea indicated that there are stage-specific patterns, and that certain protein species are prominent in early stages, but become unresolvable in later stages where different species have assumed prominence. Direct analysis of stage-specific gene expression as indicated by patterns of short-term protein synthesis also suggest that some of the major synthetic activities change qualitatively as development progresses. These alterations are discussed in the light of the changing cellular populations within the gland and certain correlations are proposed. These studies support the view that the submandibular gland exhibits several distinguishable differentiated states in the course of its development.