The response to salt spray and soil salinity of two sand dune strandline species (Cakile maritima Scop. and Salsola kali L.) and two salt marsh strand‐line species (Atriplex hastata L. and A. littoralis L.) was compared in sand‐compost cultures. The growth of the salt‐marsh species remained unaffected, while the growth of the sand dune species Cakile maritima was strongly reduced by NaCl (150 and 300 mM) absorbed via the root system. All four species were resistant to airborne salinity, and under conditions of low soil fertility, salt spray increased the dry matter production, especially of the sand dune species. Mineral analysis revealed foliar uptake of Na, K, Cl, Ca and Mg. Na and Cl ions absorbed from seawater droplets induced succulence. Both salt spray and soil salt increased the methylated quaternary ammonium compound content in the shoot tissue. Under non‐saline conditions a considerable amount of these osmotic solutes was still present, while turgor pressure potential in these plants was rather low. The relation between salt, compatible osmotic solutes, turgor pressure potential and growth is discussed. Next to the major constituents of seawater, Na and Cl, especially magnesium and to a lesser extent, calcium, accumulated in the shoot tissue. Based on the positive growth response of the sand dune species to airborne salt, they should be termed ‘aerohalophytes’, whereas ‘soil halophytes’ should be used when referring to the Atriplex species, which are more specifically adapted to the increased salinity of salt marsh soils.
Salt secretion, salt accumulation and transpiration were simultaneously measured in salt-secreting and non-salt-secreting halophytes and glycophytes. The sodium content of the xylem sap was calculated. It is concluded that salt-secreting halophytes differ considerably in their sodium secretion rates, but less in their sodium exclusion capacity. Salt-sensitivity of the non-secreting species was related to a comparatively high sodium xylem content (15.1 mM Na). Transpiration rates are remarkably similar for all species. It is argued that the distinction between salt accumulators and salt excluders is not only based on differences in ion exclusion but is also related to the capacity to accumulate compatible osmotic solutes.In experiments aiming at an ecophysiological comparison of the mineral and water economy in relation to halophyte zonation, secretion, accumulation of sodium and transpiration were simultaneously measured in four salt-secreting and four non-salt-secreting halophytes and glycophytes. Plants were grown in a greenhouse (20°C, 65% RH; 6-18 hr light 7000Lux) in 0.25 strength Hoagland's solution with 0.2 M NaCI added. Salt secretion was measured by rinsing the leaves with distilled water over a 6 day period. Relative humidity of the air was kept at 65% in order to avoid the loss of secreted salt through run-off from the leaves,which occurs under more humid conditions (ROZEMA & RIPHAGEN 1977). Transpiration rates were determined by weight measurement for a 48 hr period. The total weight of the plants which were precultured for four weeks on NaCIfree0.25 strength Hoagland increased only slightly during the 6 day period. After harvesting and drying, the sodium content of the whole plant was determined by flame emission spectrophotometry. The sodium content of the xylem sap was calculated from the equation: . t ti I secretion + accumulation Ion concen ra IOn xy em sap = -----' ---------transpirationThe results are summarized in table 1, and it may be concluded that even the glycophytic species Juncus articulatus has the ability to exclude sodium ions to some extent since the rooting medium concentration (200 mM Na) is ten times reduced. In the non-secreting halophyte Juncus maritimus the sodium content of the xylem sap is even a factor 150 lower than that of the culture medium.Obviously the stronger exclusion of sodium ions in Juncus maritimus relates to its
SUMMARY The disease in the carnation here commonly referred to as “Wilt” or “Crown‐rot” is caused by a fungus belonging to the genus Fusarium. The disease usually shows as a wet rot of the stem just below the soil. The lower leaves turn a sickly colour, are usually more erect and soon the whole plant is dead. This fungus was isolated from diseased carnations; grown in the laboratory and when inoculated into healthy plants produced the disease. The organism grew well on all culture media, producing usually a greyish growth. Along the glass of the tubes and the bottom of Petri dishes, it showed shades of grey, yellow, brown and red. The fungus grows best at 25o‐30o C, with something in favour of the latter temperature. No growth at 0o C. or 40o C. At 15o C. growth less vigorous than at 25o C.: at 37o C. it remains feeble. The fungus is not killed by incubation at 0o C.; cultures from 0o C. and 37o C. transferred to 30o C. showed a vigorous growth. No growth occurred in cultures transferred from 40o C. to 30o C. The organism appears to be strictly aerobic. It withstands high degrees of acidity but less alkalinity. Conidia vary in size in different media and range between 14.85‐37.95μ× 3.3‐6.6μ, hyaline, fusiform to nearly straight, on some media (banana) very small; 2–6 celled. Experiments were carried out in the laboratory with various disinfectants and fungicides; these experiments serve to act as a guide for experiments on the treatment of infected soil. Field experiments carried out with the object of finding whether the application of quicklime or formalin solution to diseased soils would have any beneficial effect, tend to show: (a) the plot treated with formalin was no better than the control plots; (b) on the whole, the plots treated with quicklime fared a little better than the controls, but further experiments would be necessary. It is urged that the spread of the disease should be prevented as far as practicable by: (a) growing one's own cuttings; (b) obtaining cuttings from healthy vigorous plants only; (c) laying Guttings in in healthy ground; (d) pulling up and destroying all plants showing any evidence of disease, Diseased soil should be submitted to a judicious process of crop‐rotation for a few years, and all attempts made to prevent the fungus spreading from diseased to healthy areas. The question of the existence of varieties more or less immune from the disease has thus far not received attention, though it is a problem well worth serious consideration, and the breeding of disease‐resistant varieties may yet be the ultimate solution.
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