Light Effects on Apical Dominance

Reducing light intensity from 18·0 klx to 5·4klx promoted main-stem growth in Phaseolus vulgaris but leftlateral extension unaffected. Shading individual laterals orapices of main stems promoted elongation of the shaded portion.Increasing day length from 8 to 16 or 24 h did not greatly affectplant growth if full-intensity and full-spectrum light was used.If, however, the additional light was supplied by incandescenttubes containing a high proportion of infra-red light, growthof main stems but not laterals was induced in proportion tothe length of the additional light period. It is suggested thatthe increased growth of the main stem in response to infra-redlight prevented the equivalent response of the laterals becauseof the enhanced ability of the main stem to suppress lateralelongation.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

Viral Properties of Scrapie

ALTHOUGH scrapie agent has many unusual features^1–4, some aspects of its behaviour are analogous to viral properties⁵. The manner in which the agent invades the nervous system after peripheral inoculation immediately recalls such typically neurotropic viruses as poliomyelitis or rabies. After inoculation into the fore-limb changes occur first in the cervical cord; following injection into the leg they appear first in the lumbar cord⁶. We now report another way in which scrapie behaves as a classical virus.     

Localization of Tumour Specific Antigen on External Surface of Plasma Membrane

FOLLOWING the adventitious finding that lymphocytes from patients with malignant (but not benign) neoplasia are sensitized to encephalitogenic basic protein of myelin (EF)¹ and to a protein similarly extracted from a variety of tumours², a logical step would be to determine the subcellular localization of the specific antigen(s) on or within the cancer cell and whether or not the antigen continues to be associated with human malignant (or transformed) cells long maintained in culture. If this were so, then such cultures might serve as a convenient and standard source for an antigen of considerable potential in the diagnosis—and perhaps also the treatment—of malignant disease. The allied question of the identity and uniqueness of the antigens extractable from different cell lines or tumours will be the subject of a separate communication.     

Guild structure in solitary spider-hunting wasps (Hymenoptera: Pompilidae) compared with null model predictions

Abstract.

• 1 Three aspects of prey utilization are documented in a guild of spider-hunting pompilid wasps at a Breckland heath site: female phenology, size, and microhabitat utilization.
• 2 Twenty-four species were present at the site, 59% of the British fauna. Ten species individually represented more than 1% of the guild.
• 3 Pompilid abundance peaked in early July and mid-late August. Anoplius viaticus had a different life-history from other common guild members, making its inclusion in the guild questionable.
• 4 Most species represented by large samples occurred in all microhabitats and time intervals, and all species overlapped in size with all other species except A. viaticus. Arachnospila anceps was numerically dominant in all microhabitats and most time intervals.
• 5 Mean pair-wise overlaps in phenology and microhabitat utilization were significantly lower than predicted by null models, consistent with the idea that interspecific competition has been important in determining guild structure.
• 6 Female size is highly correlated with prey size, but the distribution of mean female sizes did not generally differ from null expectations.
• 7 Interpretation of comparisons with null models is problematic, particularly because it is difficult to quantify evolutionary ‘favourability’ of different resource states. Null models are currently of limited use because the patterns expected to result from key processes such as competition are uncertain in multi-dimensional systems.