Effects of Nitrogen Supply on Bulb Development in Onion Allium cepa L.

Onions were sub-irrigated with 0.6, 2.4, 4.8 and 12 mol m^–3nitrate while growing in constant photoperiods of 14, 15 or16 h. The lower the nitrogen, the later bulb scale initiationoccurred and in 14 h photoperiods bulb scales initiated onlyat the highest N level. In the early stages of the experiment,the ratio bulb width/neck width was higher in low N than inhigh N treatments, but the reverse was true at the later harvests,by which time bulb scales had formed. In a second experimentonions were sub-irrigated continuously with 0.6 mol m^–3or 12 mol m^–3 nitrate or transferred from the low to high,or from high to low N after 36 d of growth in 14, 15.25 and17 h photoperiods. An initial period of low N delayed bulb scaledevelopment and ripening relative to high N throughout, particularlyunder 14 h photoperiods. Late N deprivation did not preventor delay bulb scale initiation or ripening. In a field experiment,plants not fertilized before sowing but given the total quantityof N late in the growing season formed mature bulbs later thanplants fertilized with N before sowing, or given half the quantityof N before sowing and the second half late in the growing season. Key words: Onion, nitrogen, photoperiod, daylength, bulbing     

Experimental tissue cyst induced Toxoplasma gondii infections in dogs

Tissue cyst induced Toxoplasma gondii infections were examined in 2 beagle dogs orally inoculated with tissue cysts. Neither dog developed clinical signs of toxoplasmosis. Both dogs developed low antibody titers to T. gondii. The MAT and IFAT were superior to the LAT and IHT tests for detecting antibodies to T. gondii.     

The mating behaviour of the honeybee (Apis mellifera L.)

An account is given of the mating responses of free-flying drones towards a queen, and of the pheromones controlling these responses.