Galling by Dysaphis devecta benefits groups of Aphis fabae as they are larger both on control and nitrogen‐deprived apple plants which have been galled. Presumably D. devecta gains these advantages for itself because it can produce galls. Honeydew from A. fabae feeding on galled and ungalled control apple plants of the same age differs in its amino‐acid content. It is thought that the presence of larger amounts of amino acids in the honeydew of aphids feeding on galled plants indicates that they had access to a better supply of these essential nutrients and consequently were able to attain a larger body‐size. Résumé LA CROISSANCE D'APHIS FABAE, INDICATEUR TÉMOIN DE L'AVANTAGE NUTRITIONNEL ASSOCIÉ À LA FORMATION DES GALLES, POUR LE PUCERON DU POMMIER DYSAPHIS DEVECTA Le puceron Dysaphis devecta Walker provoque des galles rouges sur les feuilles du pommier. Il n'est pas possible d'évaluer les bénéfices que peuvent offrir à ce puceron cette formation de galles, mais si on élève sur ces mêmes feuilles Aphis fabae Scop. qui lui ne provoque pas de galles, alors on peut constater que la formation de galles est bénéfique pour cette dernière espèce. Deux lots de ces pucerons ont éTÉ élevés sur des jeunes pommiers âgés de deux semaines, un lot se composant uniquement de cinq larves d'A. fabae, l'autre comportant quatre larves d'A. fabae et une de D. devecta. La même expérience a éTÉ répéTÉe pendant quatre générations avec les descendants de chacun de ces lots de Puceron. Dans toutes les générations la longueur moyenne des pucerons élevés sur les plantes attaquées simultanément par un individu de D. devecta était supérieure à celle des pucerons issus de lots se composant seulement d'A. fabae. En même temps les Aphis fabae des lots mixtes se développaient plus rapidement et moins d'ailés sont apparus. D'autres essais ont éTÉ réalisés de la même façon, mais les plantes étaient âgées de cinq semaines et avaient reçu des solutions nutritives complètes ou sans azote. A nouveau, l'influence de D. devecta sur la plante‐hôte a entraîné une alimentation plus favorable pour Aphis fabae pendant quelques générations. Le miellat d'A. fabae s'alimentant sur des plantes de même âge, attaquée ou non par D. devecta diffère par sa teneur en acides aminés; celle‐ci est plus élevée dans le miellat des pucerons se nourrissant sur des feuilles portant des galles. La production de galles foliaires par D. devecta favorise done la production d'acides aminés ce qui est bénéfique pour ce puceron gallicole.

A screening method is described whereby potato plants are grown in soil in closed plastic containers in the dark, producing root systems upon which potato cyst nematodes can reproduce. Tubers are planted in John Innes No. 2 compost at 30% moisture and inoculated with an egg suspension. The canisters are held at 20 OC for S.E.D. Medium f 6.5 Clones t 13.8 Medium x clones

Sulphoevernan is a sulphated ~-1 --, 3, 1 -, 4 polyglucan (Mr 20000) with a helical structure. This compound effectively inhibits both human immunodeficiency virus type 1 (HIV-1) and type 2 infection of cells in vitro at concentrations around 0-5 ~tg/ml. Moreover, the compound completely inhibits HIV-l-induced syncytium formation at a concentration of 1 ~tg/ml. Competition experiments with 35S-labelled sulphoevernan revealed that the mannose-specific lectin from Narcissus pseudonarcissus prevented binding of sulphoevernan to HIV-1, whereas the antibody OKT4A did not reduce the amount of sulphoevernan bound to MT-2 cells. These data indicate that the non-cytotoxic polymer sulphoevernan binds to the virus rather than to the host cell. In vivo studies, using Rauscher leukaemia virus in NMRI mice, revealed that, at a daily dose of 20 mg/kg, the animals were protected against virus-induced increases in spleen weight. From these in vitro and in vivo data we conclude that sulphoevernan has potential in the treatment of acquired immunodeficiency syndrome.

The honeydew of Myzus persicae feeding on radish seedlings contains glucose, fructose, trehalose, melezitose and sucrose, of which glucose and fructose are present in radish seedlings. In addition, the honeydew contains eight organic acids, of which seven are present in uninfested seedlings and six are present in infested radish seedlings: of the eighteen phenolic acids in the honeydew, five are present in uninfested radish seedlings. Auxins, gibberellins, growth inhibitors and cytokinins are present in the honeydew. The presence of carbonate and bicarbonate previously recorded in honeydew of M. persicae could not be confirmed, but ammonia is present in fresh honeydew and accounts for its high pH.

I 0 A P B 81 282 J. M. S. FORREST AND A. F. G. DIXON parallel to the midrib. D. plantaginea induces yellow or green longitudinal rolls by causing the leaf to roll downwards along its length. Illustrations of these galls are presented in Hille Ris Lambers (1945), Massee (1954), and Plate, fig. I. Selection of feeding siteAdult D . devecta and D. plantaginea were placed singly on the adaxial surface of leaves of rootstocks of apple (MM. 111) and after 48 h the position of aphids feeding on the leaves was noted. Leaf rolls caused by D . devecta and also the stems of apple seedlings infested with D. devecta and D . plantaginea were sectioned (12 pm) and stained with safranin and fast green. Culture of apple seedlingsApple seed (MacIntosh Red) was germinated in a Petri dish on filter paper treated with a solution of gibberellic acid (GA3) as previously described (Forrest, 1970). They were planted 5 days after germination and when 6-12 days old they were infested with aphids. Examination of infested and uninfested apple seedlingsUnless they are restricted to a particular area of a seedling aphids usually settle on or close to the growing point. The effect of aphids on the growth of seedlings was determined by examining the leaves, the stem between the cotyledons and the first leaf (the first internode), and the stem below the cotyledons (the hypocotyl).Leaves. Eight-day-old apple seedlings were infested with three first instar larvae of . Morphogenetic effects of light intensity and night temperature on the growth of lettuce (Lactuca sativa L.) with special reference to the process of heading.