The Secretion of the Salt Glands of Limonium latifolium Ktze

The concentration of NaCl in the external solution during the pretreatment influences the secretion by the salt glands. A pretreatment with 2 % to 3 % is most favourable, then both the amount and the concentration of the secreted fluid and also the NaCl concentration in the leaf are greatest (Table I). The rate of secretion is constant during the first few days or is reduced (Tables III, IV, V). The amount of secreted fluid is usually somewhat higher on water than on salt owing to the lower osmotic value of the external solution. The NaCl concentration of the secreted fluid may either increase or decrease during the secretion on a salt solution. With secretion on water there is always a decrease. When exposed to light the amount of secreted fluid increases. The concentration of the secreted fluid does not change (Table VI). If temperature is raised from 5 to 25° C the rate of the secretion of fluid increases 7 times. The concentration of the secreted fluid remains fairly equal, unless the secretion takes place on water (Table VII). Oxygen is required for the secretion. In a low concentration inhibitors increase the rate of the secretion of fluid, in a high concentration they inhibit it. The NaCl concentration of the secreted fluid remains unchanged (Tables VIII and IX, Fig. 2). The osmotic value of expressed leaf sap varies. The average osmotic value is equal to the osmotic value of the medium (Table XI). The osmotic value of the sap secreted by the gland is higher than the osmotic value of the expressed leaf sap (Table XI). For the secretion osmotic work is done. The osmotic value of the secreted fluid, computed as NaCl solution, corresponds with the NaCl concentration of the secreted fluid (Table VI). In an other experiment (Table XIV) with secretion on sugar plus salt solution it was greater than the NaCl concentration of the secreted fluid. This indicates the presence of other substances in the secreted fluid. Increase of the osmotic value of the external solution : (A) by sugar (Tables XII, XIII, XIV) decreases the amount of secreted fluid and increases the NaCl concentration and the osmotic value of the secreted fluid. (B) by NaCl (Table XV) alters the amount of secreted fluid but little. On addition of too much diluted salt solutions or water there is a decrease of the amount of secreted fluid. The NaCl concentration in the secreted fluid increases. The total loss of Cl has increased. (C) by MgS04 (Table XV) gives a reduction of the amount of secreted fluid and an increase of the NaCl concentration of the secreted fluid. The total loss of Cl has decreased. The mechanism of the secretion may be considered as a system that introduces salts actively into the gland cells and by doing so causes a pressure that results in a squeezing of sap through the pores out of the gland cells. The amount of expressed sap depends on the pressure in the gland cells. The latter may be osmotically influenced by the external solution. The composition of the expressed sap depends on the substances accumulated in the gland cells and on the permeability at the pores.