OBSERVATIONS ON LEAF AND BUD FORMATION IN HYDROCHARIS MORSUS-RANAE

Regular sequences of leaf and bud formation occur in several members of the Hydrocharitaceae, including Hydrocharis, in which buds are normally formed in the axil of every second leaf of the phyllotactic spiral. Leaf inception begins by periclinal divisions of the inner cells of the 2-layered tunica. Bud formation, which occurs in the apical meristem itself, immediately following the inception of the subtending leaf primordium, begins by divisions in various planes in the corpus, the 2 tunica layers remaining continuous throughout. The young bud meristem soon gives rise to a lateral bud, before leaf formation begins upon it. Because of these and other features, this species is one of considerable morphogenetic interest. Morphogenesis of the whole plant, and in particular the factors controlling the regular sequence of leaf and bud formation, have been and are being investigated experimentally.     

THE INCIDENCE AND CONTROL OF CAULIFLOWER MOSAIC IN BROCCOLI IN SOUTH-WEST ENGLAND

Cauliflower mosaic in south-west England is most prevalent where there is a sequence of brassica crops that overlap in time. Broccoli yields can be increased by using plants raised in seed-beds separated by half a mile from old infected plants. Surrounding seed-beds with crops of kale or barley decreased the incidence of mosaic even when the seed-beds were only 5 yd. from infected plants.
Most plants infected at harvest contract infection after transplanting. A plant infected in the seed-bed or early in the growing season can produce a group of infected plants immediately around it, and almost as many farther away. Spread can occur in the same pattern from these secondarily infected plants.
Loss of yield is correlated with the time plants are infected. Plants infected as seedlings produce little or no curd or seed, whereas those infected when nearing maturity yield almost as well as uninfected plants.
The movement of alate aphids is positively correlated with the numbers of infectedplants, and symptoms in field plants generally appear 8–9 weeks after infection.
Cauliflower mosaic virus occurs in strains distinguishable by the severity of symptoms they cause.     

OBSERVATIONS ON BLINDNESS IN OATS

The relative importance in North Wales of various factors said to cause blindness in oats was investigated. It is concluded that a direct attack on the developing panicles by frit fly larvae and by adults and larvae of thrips was of little importance in causing the blindness encountered. Most of the blindness appeared to result from adverse physiological conditions probably operative during early growth. Varying varietal susceptibility to blindness was noted, and the effect on the subsequent panicles of an early insect attack on the vegetative parts of the plant is discussed.     

OBSERVATIONS ON YELLOW ROT IN HENS'EGGS

SUMMARY: A yellow rot of fresh hens'eggs has been investigated and it is concluded that the fault is not of bacterial origin. Enlarged yolks with a high pH were frequently encountered, constituting 34% of the yellow rot eggs examined.     

OBSERVATIONS ON SNOW ALGAE IN CALIFORNIA1,2

Algae that impart a red color to snowfields are rather common in California. Red snow occurs mainly in the Sierra Nevada at altitudes of 10,000–12,000 ft (3050–3600 in) and can occur at high altitudes where snow persists in other parts of the state. The distribution in the Sierra was similar in 1969 and 1970, contrasting snowfall years. Colored snow was found from May to October in old, wet snow-fields. The predominant color was red and occurred as surface patches in depressions in the snow. The color could extend as deep as 30 cm below the snow surface. Algae in the snowfields of the Tioga Pass area (Sierra Nevada) were large, red, spherical cells of Chlamydomonas nivalis. No other algae were seen. Their distribution, as measured by cell numbers and chlorophyll a, was patchy. Algal cells and chlorophyll a were mainly distributed at or near the snow surface but extended down to a depth of 10 cm. Light intensity was greatly attenuated by snow, but enough light for photosynthesis was found at 50 cm below the surface. Nutrient content of one snow sample was very low. The populations were very actively photosynthetic and took up as much as 65% of added ¹⁴CO₂ in only 3 hr. It was tentatively concluded that CO₂ limits in situ photosynthesis. Photosynthesis was inhibited by melting snow samples. Rough calculations of the growth rate suggested in situ generation times of only a few days for these algae.     

SOME OBSERVATIONS ON THE SITATUNGA IN KENYA

A 16-month study was made of sitatunga in a swamp in western Kenya, with particular reference to distribution within the habitat, daily activity, and food preferences. Absolute figures for density could not be obtained because of observational difficulties, but there was a minimum of 7.3 animals/linear km of swamp, or c. 55/km². The sitatunga preferred areas of swamp adjacent to patches of gallery forest, and areas where there was deep water and a dense growth of tall reeds. They were most active during the first five and last two hours of daylight, and at night. Much of this time was spent feeding. Feeding behaviour and food preferences were studied. The sitatunga usually moved along well-marked tracks through the swamp vegetation; some of these led to beds of flattened plants, raised above water level, which were probably used for resting and for breeding. The latter took place in most months of the year, with a possible peak in November. Calves remained hidden for some weeks after birth. Group size and structure were examined; most sightings were of single animals or groups of two. A majority of these two groupings were composed of adult females. The proportion of immature animals seen indicated a healthy population. Courtship behaviour was observed 18 times and mating once.