PHYSIOLOGY OF THE RED MANGROVE. 637 



tion may be made that the effects were more chemical than physical 

 and so according to Sachs it would seem that sodium chloride has 

 a retarding chemical effect in addition to the retardation of its 

 physiological action in the osmosis of root absorption. However, 

 as Burgerstein says (p. 152), neither investigator carried on a large 

 series of experiments and Senebier moreover was only concerned 

 with the amount of water as indicated by the absorption. 



In connection with measuring transpiration of plants in various 

 concentrations of salts as the series in this paper, Burgerstein^^^ has 

 made a series of interesting measurements, partly with woody twigs 

 and partly with rooted seedlings in o.io to i.o per cent, solutions 

 of the following nutrient salts : potassium, calcium and ammonium 

 litrates, magnesium and ammonium sulphates, potassium phosphate 

 and potassium carbonate. In very dilute solution, .05 to 2.5 per 

 cent., the transpiration, when compared with that of plants in dis- 

 tilled water, is increased, the higher the concentration of the solu- 

 tion is increased, until at a definite concentration a maximum is 

 reached. For the corn plant (Zea mays) this is about 2.5 per cent. 

 A further interesting feature of Burgerstein's work is that this 

 maximum transpiration-concentration is lower for the alkaline salt 

 solutions and higher for the acid reacting salts than for the maxi- 

 mum point of nutrient salts with a neutral reaction. In solutions 

 above this degree of concentration the transpiration steadily de- 

 clined, so that a general rule could be deduced that in .3 to .5 per 

 cent, solutions the transpiration was already less than that of plants 

 in distilled water. 



As most of the cultures of the mangroves used in the experi- 

 ments described in the present paper were grown in much higher 

 concentrations than those of Burgerstein, the optimum concentra- 

 tion of very dilute solutions could not have been detected, or its 

 climax of transpiration increase observed. However, in the curve 

 No. I there is seen a slight sagas the percentage increases from fresh 

 water toward the 10 per cent, solution. This may be interpreted as 

 the slight increase in transpiration (here expressed in time rate) 



113 Burgerstein, A., " Untersuchungen ueber die Beziehungen der Nahr- 

 stofife zur Transpiration der Pflanzen. I. Reihe," Sitcb. der kais. Akad. dcr 

 Wiss. in IVicn, Bd. LXXXHL, p. 191, 1876. 



