An Electron Microscope Investigation into the Structure of the Floridean Pit

Ultra-thin sections of the red algae Rhodymenia palmata andLaurencia caespitosa were examined in the electron microscopein order to determine the fine structure of the Floridean pits.The pits found in the two species examined are shown to be quitedifferent from each other, in Rhodymenia the pit is open sothat the cytoplasm is continuous through the cell wall, whilstin Laurencia the pit is completely closed by a lamella of thecell wall. These two types are shown to be equivalent to thosedescribed by Jungers (1933) on the basis of light microscopeobservations.     

Drought limitation of photosynthesis differs between C3 and C4 grass species in a comparative experiment

Phylogenetic analyses show that C₄ grasses typically occupy drier habitats than their C₃ relatives, but recent experiments comparing the physiology of closely related C₃ and C₄ species have shown that advantages of C₄ photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in grass species representing the known evolutionary diversity of C₄ NADP‐me and C₃ photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C₄ grasses in control treatments were characterized by higher CO₂ assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C₃ than C₄ species, and photosynthetic water‐use and nitrogen‐use efficiency advantages held by C₄ species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C₄ than C₃ grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic‐type. This phylogenetically controlled experiment suggested that a drought‐induced reduction in the photosynthetic performance advantages of C₄ NADP‐me relative to C₃ grasses is a general phenomenon.     

A revision of the babbler genus Trichastoma and its allies (Aves: Timaliinae)

By means of a comparative analysis of 12 morphological and behavioural characters, the timaliine genus Trichastoma and its relatives in the tribe Pellorneini are revised to reflect new understanding of inter- and intrageneric relationships (cf. Mann et al. 1978). Trichastoma as constituted by Deignan (1964) is here subdivided into three unambiguously monophyletic genera, the Malayan Trichastoma and Malacocincla , and the African Illadopsis.
Evidence is presented indicating that the reconstituted Trichastoma should be considered the stem genus for the tribe. Reviewing the distribution of morphological and behavioural characters, the general implication is that the African forms share a recent common ancestor with those from Asia. Distributional data support the contention that the group originated in the Malayan region and colonized westward through southern Asia and Arabia to Africa (probably in early Quaternary) when humid and warm conditions fostered a continuous Afro-Asian corridor of tropical wooded habitats. The postulated greater age of the pellorneine assemblage in Malaysia, along with the region's insular geography, has fostered a larger species radiation than that in continental Africa. Recent desiccation of Arabia and central and northwestern India probably caused widespread regional extinction of linking forms and has isolated the Pellorneini into two humid forest refuges in equatorial Africa and eastern Asia.     

Effects of Sodium Selenite on the Growth of Bracken Fern Root Callus

Sodium selenite promotes the growth of bracken fern root callusgrowth over a narrow, low range of concentrations, while higherconcentrations are strongly inhibitory. Pteridium aquilinum, bracken fern, sodium selenite, selenium, callus     

An Electron-microscopic Investigation of the Walls of Conifer Cambium

Electron-micrographs of the primary walls of conifer cambiumreveal the type of structure already found in other primarywalls, except that no area of ‘loose’ microfibrilsappear to be present. In addition, groups of fibrils are visibleradiating from a centre which appears to be granular and recallingstrongly the putative islands of synthesis reported in Valonia.