Oviposition behaviour is important when modelling the population dynamics of many invertebrates. The numbers of eggs laid are frequently used to describe fecundity, but this measure may differ significantly from realised fecundity. Oviposition has been shown to be important when describing the dynamics of slug populations, which are important agricultural pests. The numbers of eggs laid by Deroceras reticulatum and their viability were measured across a range of 16 temperature (4, 10, 15 and 23°C) by moisture (33%, 42%, 53% and 58% by dry soil weight) experimental combinations. A fitted quadratic response surface model was used to estimate how D. reticulatum adjusted its egg laying to the surrounding temperature and moisture conditions, with most eggs being laid at a combination of 53% soil moisture and 18°C. The number and proportion of viable eggs also covaried with temperature and moisture, suggesting that D. reticulatum may alter their investment in reproduction to maximise their fitness. We have shown that the number of viable eggs differs from the total number of eggs laid by D. reticulatum. Changes in egg viability with temperature and moisture may also be seen in other species and should be considered when modelling populations of egg‐laying invertebrates.

Summary Extracts from anaerobically decomposed shoots of a range of grass species were toxic to other grasses and clover. This phytotoxicity was less after 20 days than after 10 and seemed to be caused by organic acids. The residues produced by Festuca rubra, Alopecurus pratensis and Agrostis stolonifera were the most toxic. After aerobic decomposition for 10 days extracts from these three species were phytotoxic, but after a further 10 days decomposition they caused a stimulation in grass and clover root growth. These results are discussed in relation to the poor establishment that sometimes follows reseeding old pasture land.

Application of 6-benzylaminopurine to cucumber leaves before inoculation with Colletotrichum lagenarium substantially decreased lesion development; decrease was accompanied by an increase in certain plant metabolites. Leaves systematically protected from infection by C. lagenarium by earlier inoculation with the same pathogen showed similar decrease in lesion size without increases in these metabolites. ZusammenfassungDurch 6-Benzylaminopurin induzierte Resistenz gegen Colletotrichum lagenarium in der Gurke Die Behandlung von Gurkenblattem mit 6-Benzylaminopurin vor der Inokulation mit Colletotrichum lagenarium fiihrte zu einer erheblichen Verminderung der Entwicklung von Lasionen. Dies wurde begleitet von einer Vermehrung bestimmter Pflanzenstoffwechselprodukte. Blatter, die schon zu einem fruheren Zeitpunkt mit dem gleichen Pathogen infiziert worden und daher systemisch gegen Infektion mit C. lagenarium geschlitzt waren, zeigten zwar einen ahnlichen Ruckgang der Lasionengrofie, jedoch keine Zunahme dieser Stoffwechselprodukte.Changes in the resistance of cucumber plants to Colletotrichum lagenarium can be induced by inoculation with various pathogens (KuC, SHOCKLEY and KEARNEY 1975, JENNS and KuC 1977, CARUSO and KuC 1979. Cytokinins have been linked with acquired resistance in tobacco hypersensitive to tobacco mosaic U.S. Copyright Oearance Center Code Statement: 0031-9481/86/1601-0011$02.50/0 12 MILLS, GUSSIN and WOOD virus (TMV) because application of kinetin suppressed the formation of local lesions by TMV (BALAZS, SZIRAKI and KIRALY 1977). ANDEBRHAN (1978) found that kinetin affects the development of C. lagenarium in cucumber. The present study investigated the effects of 6-benzylaminopurine on lesions caused by C. lagenarium and associated changes in levels of certain plant metabolites. Materials and Methods Plants and fungiGucumber plants cv. Baton Vert and Colletotrichum lagenarium (Passer.) Ell. & Halsted were grown as described by MILLS and WOOD (1984). 6-benzylaminopurine was added to 25 ml liquid medium (MILLS and WOOD 1984), at 0,0.1,1.0 and 10 mg H in 100 ml Erlenmeyer flasks. Flasks were incubated for 8 days at 26 °G on an orbital shaker (80 r.p.m.). Gultures were filtered and fungal material dried in an oven at 110 °G until constant weight.

SUMMARY Acetic acid was applied to localized regions of barley roots. Treating a single root tip with a small concentration (5 mol m−3) of the acid stimulated root and shoot growth. No stimulation was observed when more than one root was treated or with greater concentrations of the acid. Treating 2 cm lengths along the root axis distal to the root tip region (2 cm long) gave a greater inhibitory effect on root and shoot growth than the corresponding root tip treatment. Treatment of tips and 2 cm lengths resulted in some compensatory growth in the non‐treated roots.

Fusarium culmorum was grown on different natural substrates and its subsequent pathogenicity towards wheat, barley and ryegrass studied. This fungus caused more inhibition of plant growth of all test species when grown on root residues than when present as a spore suspension in sand. More wheat seedlings were killed when sown into infected ryegrass root residues than when sown into infected wheat or barley residues. However, when ryegrass was sown into infected ryegrass roots no plant death occurred compared with over 50% when sown into infected wheat or barley. Dressing ryegrass seeds with a formulation containing calcium peroxide gave some control of F. culmorum. These results are discussed in relation to the problems that can sometimes occur following reseeding of grassland.