A review of the Cucurbitaceae

Progress in studies of Cucurbitaceae since 1964 is reviewed, particular attention being paid to the roles of seed-coat anatomy, palynology and phytochemistry in elucidating the taxonomy of the family; to the use of wild species and land-races as sources of horticulturally desirable traits for the improvement of crops; to the potentialities of wild species for domestication as new crops for tropical areas, and to the biology of reproduction, sex control and sex expression. The classification of the lady is outlined, illustrated by discussion of the more important members of each tribe, and a revised classification of Cucumis is presented.     

Biomass and annual production of the freshwater mussel Elliptio complanata in an oligotrophic softwater lake

SUMMARY. An extensive survey of Mirror Lake, New Hampshire, was carried out by divers with SCUBA to assess the importance of the freshwater mussel Elliptio complanata in this softwater lake ecosystem. Density (0.032 adults m⁻²), biomass (52 mg m⁻² as dry organic matter) and annual production (6.4 mg m⁻² as dry organic matter) of the mussel population are low when compared with results from other studies, corresponding with the general observation that mussels are scarce in soft, oligotrophic waters. We reject the traditional view that the low mussel density is a result of low calcium concentrations in Mirror Lake, and propose that mussel populations may be regulated by a scarcity of appropriate fish hosts in unproductive lakes. Elliptio complanata is probably not important in the metabolism or biochemistry of the Mirror Lake ecosystem.     

Cation-impermeable Inside-out and Right-side-out Vesicles from Human Erythrocyte Membranes

The two surfaces of a membrane can be compared by isolating sealed vesicles which bare one side or the other to impermeable probe molecules. For this purpose, inside-out (IO) and right-side-out (RO) vesicles have been generated from human red blood cell membrane ghosts and partially resolved on dextran density gradients¹. We now report further characterization of this system, showing (a) that vesicles can be made which are impermeable to small solutes, including Na⁺ and K⁺, even though the parent ghosts are quite unsealed; (b) that the dextran gradient fractionation serves to separate sealed vesicles (which happened to be IO and RO, respectively, in the original study¹); (c) that impermeable RO vesicles form instead of IO vesicles if the published protocol is modified by the untimely addition of trace divalent cations; and (d) that the vesicle fractions can and must be accurately monitored for sealing and orientation to avoid misinterpretations such as those encountered in a previous sidedness study².     

Sexual behaviour of the genus Equisetum, subgenus Hippochaete

When grown for long periods in axenic single spore cultures, gametophytes of the four European species of subgenus Hippochaete are initially male or female. Females invariably produce antheridia as they get older, but archegonium formation by males is a much rarer event and was only observed in E. hyemale and E. scirpoides. Male gametophytes are smaller, grow more slowly than the females and in E. hyemale and E. variegatum are often short-lived. The proportions of male and bisexual individuals are relatively constant within each species but vary between species. Likewise species differ in the rate at which females later produce antheridia. Gametophytes grow in three ways: activity of antheridial meristems which are totally committed to the formation of male tissues, activity of cushion meristems which may produce archegonia for an indefinite period or switch to antheridium formation, and proliferation from lamellae. Either archegonia or antheridia may arise on the adventitious branches resulting from lamellar proliferation, but the type of sex organ produced is strongly influenced by the culture medium, the sex and age of the parent tissue and the particular species in question. Only by this means are archegonia formed on initially male individuals. The sexual behaviour of the subgenus Hippochaete is compared in some detail with that of the subgenus Equisetum and several subgeneric characteristics are outlined.     

The complementary effects of plant resistance and the choice of sowing and harvest times in reducing carrot fly (Psila rosae) damage to carrots

The benefits of combining a partially-resistant carrot cultivar with different sowing and lifting dates to reduce carrot fly, Psila rosae, damage were investigated at Wellesbourne in 1983 and 1984-85. The partially-resistant cv. Sytan was less damaged and supported fewer insects than the susceptible cv. Danvers on all lifting dates. The estimated reduction of carrot fly larvae on Sytan compared with Danvers ranged from 33 to 95%. Nine combinations of sowing and lifting dates provided more than 75% marketable roots of Sytan compared with only three combinations of dates for Danvers. An early June sowing of both cultivars provided roots of a marketable size with the least attack. More than 90% of Sytan roots were still marketable in December and fewer insects were produced by the end of the season on these roots than on those sown earlier. In addition, sowing in June decreased the number of pupae produced on cv. Danvers by 10 times compared with earlier sowings. Combining partial resistance with specific sowing and lifting times enabled satisfactory yields of marketable carrots to be obtained in a field infested by high populations of carrot fly.     

Host ranges, symptoms and amino acid compositions of eight potexviruses

The host ranges, symptom expression and coat protein compositions of eight definitive potexviruses are described and compared. Only limited host range similarity was observed: clover yellow mosaic virus and white clover mosaic virus shared 11 of the 28 host species tested; foxtail mosaic virus and narcissus mosaic virus infected monocotyledons; barrel cactus virus and viola mottle virus had narrow host ranges but had eight of the host species in common. Amino acid analyses of coat proteins showed some similarity among the viruses tested, but little correlation with the different host range types. There was more variation of structurally important amino acids such as lysine, arginine, leucine and proline than might have been expected, but high alanine and low tyrosine, tryptophan, cysteine and methionine were typical of plant virus coat proteins.     

Relationship between the concentration of chlorogenic acid in carrot roots and the incidence of carrot fly larval damage

Chlorogenic acid (1·24-3·36 mg/g) was identified as the main phenolic component in the peel of carrots by hplc analysis. The higher the concentration of chlorogenic acid in different cultivars the greater the susceptibility to carrot fly larval damage. Increases in concentration were found both after carrot fly damage and after carrots had overwintered in the field. The presence and location of chlorogenic acid was confirmed in sections of carrot tissues, mounted in 0·05 M ammonia solution by viewing them using a u.v.-epifluorescent microscope. The importance of phenolic compounds and their function in the production of insect cuticle is discussed in relation to the different concentrations of chlorogenic acid and resistance to carrot fly in carrots.