Aspects of the Phænogamic Vegetation of Rodriguez,with Descriptions of new Plants from the Island.

As regards the history of its flora, the island of Rodriguez bears a striking resemblance to St. Helena. We read of the latter island that fire, goats, and finally introduced foreign plants well nigh exterminated the indigenous flora; and the same causes have operated and, I regret to say, are still operating in Rodriguez. The result is that the primitive vegetation has been in great part destroyed, leaving the island a field for the rank and rapid growth of common tropical weeds. The old and luxuriant vegetation of two hundred years ago—thus quaintly described by Leguat*, “We could hardly take our eyes off from the little mountains of which the island entirely consists; they are so richly spread with great and tall trees,” and, again, “‘Tis as I have hinted, composed of lovely hills covered all with fine trees whose perpetual verdure is entirely charming”—has now, to a large extent, disappeared, and is represented by only a few species, many of which are confined to the more unfrequented and less accessible places. It is indeed difficult to recognize in the barren and arid Rodriguez of the present day the “little Eden,”“lovely isle,”“earthly paradise” of Leguat. The flora, as it now exists, is an exceedingly fragmentary one; it is therefore a matter of some difficulty to determine its exact limits and to draw conclusions as to its affinities with the floras of other oceanic islands and of adjacent continents. This is the more to be regretted, as, from the geographical position of the island and the physical condition of climate to which it is subject, its flora might be expected, whether taken singly or as part of that of the Mascarene group, to contribute very important data towards the solution of the problem of the distribution of plant‐life in that region. The following general statements may, however, be made:—     

A VIRUS DISEASE OF RED CURRANT (RIBES RUBRUM L.)

A virus causing ringspot patterns and vein clearing of red currant leaves is reported. It is inactivated at 66–68°C., tolerates a dilution of 1:2000 but not 1:5000, loses infectivity after 7–9 days in vitro and has been transmitted only by sap inoculation.
The virus infects plants in a wide range of families, resulting in chlorotic and necrotic symptoms. On Nicotiana tabacum it causes local and systemic symptoms of the ringspot type. Its host range and physical properties differ from other viruses causing ringspot symptoms, and the name red currant ringspot virus is therefore suggested.     

The moisture content of timber in relation to attack by Lyctus powder-post beetles

The relation between moisture content of oak sapwood and rate of development of Lyctus brunneus has been investigated at 23C. Oviposition took place normally in samples of various moisture contents between 5.5 and 23.5%. The eggs hatched in wood of 7.7% moisture content, but not of 61% moisture content, although the embryos developed fully. The rate of gain in weight of young larvae increased to a maximum as the moisture content of the wood rose to about 14.2% and then fell again. The rate of development from egg to adult followed a somewhat similar curve with a maximum at 16% moisture content. At all moisture contents the first male emerged a few days earlier than the first female. The average weight of the male beetles was less and their moisture content greater than those of the corresponding females. The average weight of the beetles showed a tendency to increase at moisture contents of the wood above 97%. The average moisture content of the males was fairly constant up to 156% moisture content of the wood, but that of the females rose slowly as the moisture content of the samples increased. In wood of 15.6% moisture content at 23C. the minimum period of development from egg to adult was 167 days; at 14.2% moisture content and 27.5 C. this was reduced to 142 days. Green timber was shown to be liable to infestation as soon as a superficial skin was formed of a suitable moisture content; the upper limiting moisture content is probably the fibre saturation point. Control of moisture content of timber cannot be achieved sufficiently easily for it to become an important method for the control of Lyctus infestation.     

Field studies of potato-root eelworm, Heterodera rostochiensis Wollenweber, 1938-40

Field studies of potato crops under different soil and fertility conditions and exposed to attack by diverse concentrations of potato-root eelworm led to the following conclusions:
In the north-western agricultural advisory province potato-root eelworm is not a major cause of failure or partial failure of potato crops on land where the viable cyst concentration is low (under 10/10 c.c. of soil). On such land increased yields can be obtained by improving conditions for plant growth, widening the rotation and increasing the fertility of the soil.
The production of satisfactory crops on land with a low eelworm population is likely to be accompanied by considerable increases in the numbers of root eelworms in the soil.
Crops free from signs of 'potato sickness' or 'potato-root eelworm disease' can be grown on land heavily infested with root eelworms (viable cyst concentration exceeding 25/10 c.c.), if no other adverse condition, such as unsuitable weather, lack of available food or incidence of fungus disease, affects the growth of the crop, but yields from heavily infested land are not likely to be more than moderate.
The treatments used against eelworms in the trials described here did not give results commensurate with their cost.
The practical difficulties of incorporating lethal substances with soil in the field are considerable, and this may have contributed to the disappointing results obtained.
The study of the influence of host variety on cyst production suggests that varietal differences in the host plants may influence the numbers of cysts formed on the crop, but the evidence is not conclusive.