NOTE 69 (page [366])
On the Germination of Cuscuta
My observations were made on the Hawaiian endemic species (C. sandwichiana) and on a Fijian introduced species. Germination occurs readily in fresh water, the floating seedling growing rapidly. When the germinating seed is placed on wet soil in the shade, the seedling grows at the rate of 3⁄4 inch (19 mm.) a day. The store of nutriment contained in the swollen radicular end will support the seedling for a couple of days, and if it has not then found a host it withers and dies. At first lying prone the seedling then lifts its upper end into the air, and it was almost pathetic to notice it moving round and round, endeavouring vainly to find some object near. The seedlings make no effort to strike into the soil, and when they are allowed to attach themselves to a plant they ascend rapidly, growing at the upper end and dying at the lower end.
NOTE 70 (pages [477], [480-1])
On Beach-Temperature
My data are rather scanty; but, judging from observations made in Hawaii, in South America, and in the south of England, the following scale would probably be true of typical beaches where the sand is found relatively cool and moist at a depth of four or five inches. This moisture seems to arise entirely from subsoil drainage seaward. When a beach fronts an arid, rainless region, few if any plants grow on it; the sand is loose, hot, and dry at the depth indicated; and the temperature of the surface half-inch rises to between 130° and 140° F., whilst four inches down it is 95° to 100°. Salt-marshes situated behind a beach even in a desert-region change its thermal behaviour, and it would then be more like a beach skirting a vegetated sea-border in the same latitude. The method of observation was as follows:—An unmounted thermometer of the size of a clinical thermometer, but graduated higher, was placed horizontally in the sand half an inch below the surface and a reading taken. It was then pushed vertically into the sand until the bulb was four inches deep and another reading taken. Provided that the sand is moist beneath, the colour does not seem to make much difference, except perhaps in very dark sands, none of which were tested.
Ordinary Beach-Temperatures with an Unclouded Sky in the Hot Season
during the Early Afternoon.
| Surface half-inch. | Four inches deep. | |
|---|---|---|
| Temperate latitudes about 50-55° | 100-105° F. | 77° F. |
| Sub-tropical latitudes about 30-35 | 105-110 | 80 |
| Tropical latitudes about 10-20 | 110-120 | 85 |
This illustrates only the average condition. On a calm day in the case of a beach facing south in the South of England, I have obtained exactly the same readings in July as at Valparaiso in January, 112° at surface, 80° four inches deep.
NOTE 71 (page [479])
On the Buoyancy of the Seeds or Seed-vessels of some Chilian Shore Plants
(1) Nolana, probably paradoxa. Common on the beaches of Southern Chile. The ripe drupes have a somewhat fleshy outer covering which they lose when lying on the sand, and present themselves then as dark-brown angular “stones,” often five to six millimetres across. Inside the outer hard covering of the stone is a layer of spongy tissue which gives it buoyancy; but since these coverings are wanting at the scars marking the basal insertion of the drupe, the embryo seems insufficiently protected against injury during flotation in sea-water; and the seed-vessel at first appears to be only fitted for conveyance by the currents over a limited tract of sea. However, in a preliminary experiment on seed-vessels that had been kept a few weeks, I found that 30 per cent. floated after three weeks in sea-water. Subsequently, after drying for a year, the seed-vessels were again tested in sea-water, nearly all of them floating after three months’ immersion. Two of them, removed after six weeks’ flotation, germinated healthily. These fruits are common in beach-drift between Corral and Valparaiso.