190 CARNEGIE INSTITUTION OF WASHINGTON. 



hypocotyls were ground up and extracted with distilled water and filtered. 

 The filtrates were then divided and one-half boiled several minutes. To 

 both solutions a small quantity of standard tannin was added and both 

 placed in an incubator at 40° C. for 24 hours. After allowing this time for 

 the anticipated enzyme to effect changes in the tannin content of the liquids, 

 both the control flasks and those containing the unboiled extract were treated 

 with ferric chloride to cause precipitation, with corresponding change in 

 color. In some of these tests the precipitate was filtered off and after 

 repeated washings was desiccated and weighed, but in none of the tests was 

 there any conclusive evidence of the presence of the enzyme tannase in the 

 hypocotyl of Rhizophom. 



The balance of the season, after the conclusion of the above tests, was 

 devoted largely: 



First. — To a continuation of the work on the transpiration-rate measure- 

 ment of Rhizophora seedlings planted in different conditions of soil, light, 

 and shade, and varying concentrations of fresh and salt water. These 

 seedlings were planted in large glass beakers, or jars 8 inches in diameter 

 and about 10 inches deep, 3 seedlings to a jar. These plants also were 

 secured at Bush Key of the Tortugas group in quantity sufficient to fill 

 about 50 jars. The seedlings are not plentiful in the Tortugas, most of them 

 having probably drifted from the Marquesas Atoll, and on being cast up 

 on the north and east shores of the Tortugas have taken root on the beaches 

 in the moist sand and debris of seaweed, etc., where they survive for several 

 months till the moisture fails or they have exhausted their reserve supply 

 of food in the hypocotyls. These seedlings were carefully and speedily 

 transferred in pails of moist sand to the laboratory and selected ones planted 

 in the jars. All broken and injured plants were rejected and an effort was 

 made to keep all of as uniform a size as possible. While this supply of the 

 material was limited, the plants grew much more rapidly than those used 

 in the previous year's experiments on transpiration-rate measurement. 

 These plants had been brought on the yacht from Cayo Agua, about 86 

 miles east of the Tortugas, and did not very well bear the transplanting from 

 their natural beds under the old trees in the swamp to the laboratory. 



These jar cultures were started the second day of the season's work, so 

 that the plants might make some growth and be free from the shock of 

 transplantation when time came for the transpiration-rate records to be 

 taken. The records were made mostly during the middle portion of the 

 day, so that conditions were as uniform as might be. The Stahl method of 

 estimating the rate of transpiration was used. Disks of fine filter-paper 

 were saturated in cobalt-chloride solution and dried. These papers were 

 put in a Ganong leaf-clasp and the rate at which the paper changed color 

 was noted for each test. Very striking and clear differences in rate were 

 observed in the experiments this year, as were those of the previous season. 

 The solutions and soils, however, of this season's work were different from 

 those of last year. 



The mass of records of these tests has not yet been tabulated for this 

 season's work, and no idea of the results can be given in this preliminary 

 report. Some of the plants of this series of experiments were left in 

 moist soil only, out-of-doors, over the winter period of 1915-1 G, and on 

 opening the laboratory season this year one flourishing young Rhizophora 

 plant was found to have grown 8 cm. under very adverse conditions in the 

 Tortugas climate between August 1915 and June 1916. This is the longest 

 survival of any of a series of mortality experiments which the author made 

 in the 1915 season. 



