CLUTCH-SIZE, INCUBATION AND HATCHING SUCCESS IN THE HOUSE SPARROW AND TREE SPARROW PASSER SPP. AT OXFORD

Clutch-size, incubation and hatching success were studied in P. domesticus and P. montanus in 1961 and 1963–64 at Oxford. The most frequent clutch-size was four eggs in P. domesticus and five eggs in P. montanus . With one exception, colonies of P. domesticus showed no significant annual or local variations in its mean clutch-size; in P. montanus , however, there were significant annual variations in the mean clutch-size. Both species showed a seasonal increase followed by a decrease in their mean clutch-sizes.
Partial incubation occurred during the laying period of the clutch; sufficient incubation for continuous development of the embryo was apparently achieved when the last egg had been laid in clutches of two and three eggs in P. domesticus and in clutches of four eggs in P. montanus , but when the penultimate egg had been laid in larger clutches of both species. On average, hatching in P. domesticus occurred more or less synchronously in all eggs in clutches of two and three eggs, and in all eggs except the last one laid in larger clutches; the last egg in the larger clutches hatched up to a day after the others. It is suggested that this pattern of hatching was brought about by the pattern of incubation during the laying period.
P. domesticus had a lower hatching success than P. montanus , probably because fewer of its eggs were fertile.     

Does the uniform packing of sand in a cylinder provide a uniform penetration resistance?

Sand packed to a constant dry bulk density, is frequently used as an artificial growth medium in which to simulate the effects of a constant mechanical impedance on root growth. This research aimed to determine whether conventional packing resulted in constant mechanical impedance and to test alternative packing regimes. Perspex cylinders 300 mm tall with a 49 mm internal diameter were packed with moist sand to uniform and varying bulk densities to examine which type of packing gave the greatest uniformity of penetration resistance (PR) with depth. The cylinders packed to a constant bulk density (1.48, 1.55, and 1.6 Mg m^-3) all had measured PR profiles which increased markedly with depth by approximately 1, 1.5 and 3 MPa, respectively, within the top 100 mm. Between 100–300 mm depth, these same cylinders showed reductions in PR of up to 1, 2 and 2 MPa respectively. These results show that sand packed to a constant bulk density with depth would not provide a uniform mechanical impedance to plant roots.By packing sand to different bulk densities at different depths, we obtained packed cylinders that had much more uniform PR profiles (with average values of 0.25, 1.40 and 2.30 MPa). Below a depth of 50 mm, the coefficients of variation for replicate cylinders packed in this way were 12%, 5% and 18% for the 0.25, 1.40, and 2.30 MPa treatments respectively. For experiments with single plants, the lower PR values that were unavoidable near to the surface (< 50 mm) can be avoided by sowing seeds at the base of a funnel inserted into the cylinder. Treatments such as these can provide reproducible growth media, with adequate water/nutrient and aeration status for the study of plant response to uniform mechanical impedance.     

Gas exchange characteristics and nitrogen relations of two Mediterranean root hemiparasites:Bartsia trixago andParentucellia viscosa

Plant height, light-saturated rates of photosynthesis (A _max) and foliar nitrogen concentration (N ₁) were measured forBartsia trixago under field conditions in Mallorca. All three variables were postively correlated, and were also positively related to the abundance of nitrogen-fixing legumes in the associated vegetation (putative host species).A _max forB. trixago ranged from 7.7 to 18.8 mol m^-2 s^-1; similar rates were measured for a second hemiparasiteParentucellia viscosa, and both species were within the range of rates measured for six putative hosts (10.6–19.2 mol m^-2 s^-1). Fertilization of unattachedB. trixago plants with inorganic nitrogen (ammonium nitrate) elicited neither the growth nor the photosynthetic responses observed in plants considered to be parasitic on legumes and in receipt of an enriched organic nitrogen supply. Both hemiparasites had high diurnal leaf conductances (g _s) (469–2291 mmol m^-2 s^-1) and were at the upper end of the range of those measured in putative hosts (409–879 mmol m^-2 s^-1). In contrast with the latter, high nocturnal rates ofg _s were also recorded for the two hemiparasites (517–1862 mmol m^-2 s^-1). There was no clear relationship between eitherA _max orN ₁ and eitherg _s, transpiration (E) or water use efficiency (A _max/E) inB. trixago plants. The economics of water loss appear to be independent of both the supply of nitrogen from the host and autotrophic carbon fixation.     

MIGRATION OF THE NORTHWESTERN EUROPEAN POPULATION OF THE CUCKOO CUCULUS CANORUS, AS SHOWN BY RINGING

The migration of the Cuckoo Cuculus canorus is described from recoveries of ringed birds. Young birds begin to migrate in August and most go southwards by September—those in continental Europe move southeast, south or southwest, while those from the British Isles move southeast. In spring, migrants arrive in Europe in April/May, second-(calendar) year birds doing so later than post-second-year birds. In autumn old birds depart in advance of first-year birds; and the individual bird may move stepwise through Europe. Old birds showed a marked tendency to return to the same places inhabited in previous breeding seasons, and birds ringed as nestlings subsequently tended to return to the general vicinity of the natal site.     

Differential resistance among host and non-host species underlies the variable success of the hemi-parasitic plant Rhinanthus minor

BACKGROUND AND AIMS: Rhinanthus minor is a root hemiparasitic plant that attacks a wide range of host species which are severely damaged by the parasite. Rhinanthus minor also attempts unsuccessfully to form connections to a range of non-hosts which in contrast are not damaged by the parasite; however, the underlying physiological basis of these differences is not fully understood. METHODS: Biomass of host-parasite combinations was studied, and histology, electron microscopy and FT-IR microspectroscopy were used to determine the cellular-level interactions between Rhinanthus haustoria (the parasite's connective structure) and the roots of a range of potential host species. RESULTS: Two distinct defence responses were observed in the non-host forbs Plantago lanceolata and Leucanthemum vulgare. Firstly, L. vulgare was able to encapsulate the parasite's invading structures preventing it from gaining access to the stele. This was supported by FT-IR microspectroscopy, used to monitor lignification in response to Rhinanthus haustoria. Secondly, host cell fragmentation was observed at the interface between the parasite and P. lanceolata. Growth data confirmed the non-host status of the two forbs whilst, in contrast, grasses and a legume which were good hosts showed no evidence of defence at the host/parasite interface. CONCLUSIONS: Variable resistance to Rhinanthus is shown for the first time to be controlled by cellular-level resistance to haustoria by either cell fragmentation or lignification at the host/parasite interface.     

Interactions between the hemiparasitic angiospermRhinanthus minor and its hosts: From the cell to the ecosystem

Parasitic plants can significantly influence the species to which they attach. The host response is variable however, and ranges from death of the host to no detectable effects in terms of both growth and physiology. The parasite can directly influence its hosts through resource abstraction, and indirectly by influencing inter- and intra-specific interactions. Abiotic factors interact with these direct and indirect effects to moderate the potential outcome of the host parasite interaction. This paper sets out to review a series of experiments that have been undertaken in our laboratory over a number of years that examine these effects and help us to understand mechanisms underpinning the variability in host response.     

From retrospective to predictive structure activity correlations.

Semiempirical molecular orbital (CNDO/2) calculations have been performed on 22 halogen or ?CH₃ ?CF₃ and ?OCH₃ substituted benzylamines which show PNMT inhibitory activities. In terms of the single composite variable I = |0·24μ_x+0·52μ_y| a rather good linear correlation was obtained for all the compounds.Applying the “leave-L-out” technique with random sampling, this linear correlation and another quadratic one (for 22 artificially chosen points) was re-established with the aid of the remaining compounds. They have shown only small differences in the calculated pI₅₀ values as compared to those obtained with the aid of the original correlation equation, if about half of the points were left out. This means that to obtain a stable correlation with high enough predictive power one should keep the ratio $\text{N}\text{p}$ (N number of points, p number of adjustable parameters in the equation) as large as possible.Deriving an expression for the upper bound of the probability of a chance correlation in the case of a single variable correlation equation, it has been shown that, for N equal to 22 and V (the number of variables in the variable pool) equal to 11, this probability is less than 0·01%.