638 BOWMAN— ECOLOGY AND 



due to the dilute solution, before the optimum concentration is 

 reached, after which it showed a steady decrease in transpiration, 

 or as here expressed in an increase in the time interval. In addi- 

 tion to these results as found by Burgerstein, Sorauer^^* noticed 

 that in cultures kept in solutions of concentrations above this 

 optimum or maximum point, not only was the transpiration de- 

 creased but the production of dry substance in the plants as well. 

 The whole result of the series of experiments may be said to con- 

 sist in showing the transpiration relation of the mangroves growing 

 in solutions, as plants specially adapted to such halophytic aquatic 

 conditions, that for increases of salt concentration in their media of 

 growth there is a corresponding definite retardation of the trans- 

 piration rate which may be expressed in a mathematical formula. 



Transpiration of Soil Cultures. 



The second series of cultures as outlined under the description 

 of the methods of handling the material is the series of soil experi- 

 ments. The two soils above mentioned were used and two condi- 

 tions of soil moisture content employed, i. e., plants in boxes of soil 

 merely moistened with water, and plants in jars kept flooded with 

 water. The method of taking the records and the laboratory con- 

 ditions as to light intensity, atmospheric humidity and temperature 

 were the same as for the previous experiments, as was also the 

 procedure of siphoning off the water from the jars and renewing 

 the water daily to keep down the mosquito larvae. 



The factors entering into this series of experiments are really 

 much more complex than those in the first set of cultures as that 

 involved only the salt concentration of the water, the soil (shell 

 sand) used to anchor the plants being in all the cultures the same. 

 But with the use of two soils, the one of a complex chemical nature 

 (New Jersey soil), and the two sets of soil moisture contents, the 

 problem is more complicated. The results of the experiments are 

 set forth in Graph No. 2. 



The influences on the transpiration are here due perhaps more 

 to the chemical action of elements in the solution than to physiolog- 

 ic* Sorauer, P., " Studien ueber Verdunstung, Forsch. an der Gebiet der 

 Agrikultiir-Phj'sik von Wolln}'," Bd. III., 1880, p. 351. 



