FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MULLER

Feeding of the land snail Helix aspersa (Müller) was observedat monthlyintervals. Three natural populations in Galicia (NW-Spain)were studied. At two sites only a fewplants constituted thebulk of the diet and in spring the snails' diet had the highestdiversity(H'). In the third population feeding and distributionof Helix aspersa(Müller) were observed in a small plotwith permanent patches of Urtica dioica.Nearly one half offeeding snails fed upon Urtica dioica. Most of the other observationswereon Mentha suaveolens, Ranunculus repens and Gramineae. The diversityofthe snails' diet showed seasonal variation with the maximumin the autumn months.Comparison between the availability ofthe different plant species and their contribution to thesnails'diet showed that the snails did not eat at random; Urtica dioicawas eatenmuch more than expected from its occurrence and grasseswere strongly under-represented in thesnails' diet. Temporalchanges of availability were significantly correlated with theamountseaten in the case of Urtica, but not for the other food plants.The distribution ofthe snails in the plot was significantlycorrelated with that of Urtica. Chemical analysesof the foodplants revealed Urtica as the species with the higher protein,ash and calciumcontents. The strong preference of Helix aspersafor Urtica dioica could beexplained by the value of Urticaas food or by its suitability as habitat for the snails. Thelargestproportions of green material in the snails' diet occurred inthe spring and juvenilesate more green material than adultsin the three populations. (Received 16 March 1998; accepted 30 November 1998)     

GROWTH IN MEDEOLA VIRGINIANA CLONES I. FIELD OBSERVATIONS

The pattern of clonal growth in Medeola virginiana was mapped over twelve square meters in a successional white pine forest of eastern Massachusetts. From these maps and an additional sample of excavated plants, the distances and angles of divergence of daughter ramets from the base of the parent shoot were measured for 213 plants. All clonal growth parameters were found to be highly variable in the ñeld, with coefficients of variation ranging from 17–92%. The rules describing the pattern of growth of daughter ramets were found to be considerably more complicated than previously reported (Bell, 1974). The mortality of tubers, the natural variation of parameters of growth, and the complex patterns of daughter production all call into question the ability of idealized, deterministic models of growth to predict the form of clones and the position of ramets in the field.     

FIELD OBSERVATIONS FROM THE COLONY OF HONG KONG.

The list includes 40 species not hitherto recorded for the Colony (making the present total 289 species). Several species have evidently become scarce or have ceased to breed locally in recent years.     

OBSERVATIONS ON APPLE CANKER

Field observations on leaf-scar canker of apple confirm its importance in the southwest of England: on a heavily infected tree more than 5% of the current year's growth may be damaged. Leaf scars may become infected by spores of Nectria galligena which are sucked into the tracheids of a freshly exposed scar where they develop in a relatively protected environment. These freshly exposed scars become much less susceptible to infection after approximately one hour.
Infections established in leaf scars may develop immediately into cankers or they may be confined by a suberized or gum barrier. Mycelium from some of these confined lesions may spread into the surrounding healthy tissue through growth cracks when the buds develop. The lesions extend throughout the winter and spring; usually the scars earliest inoculated are the first to show cankers. It seems possible that infections of this type might be controlled by eradicant sprays applied just before leaf-fall.