PHYSIOLOGY OF THE RED MANGROVE. 647 



relation between the amounts of dextrose and tannic acid in the 

 hypocotyls of different ages. A condensed report of this work was 

 given in an earlier paper ;^^*^ however, the methods, slightly more in 

 detail, may be appropriately described here. The seedlings, as col- 

 lected in the beds, were of assorted sizes, but all presumably of the 

 crop of the spring or late winter months of the same year. These 

 seedlings were carefully measured in regard to the length of the 

 hypocotyl, stem, internodes, size of leaves, etc., and then assorted 

 into groups of successively large growths. In making the extracts, 

 ten grams of hypocotyl seedlings of uniform size were ground up 

 in a morter with a little distilled water, just as in preparing the 

 tannase tests. Some extracts were made by boiling and others by 

 infusion, but no difference in strength was noted. After pressing 

 through cheese cloth each extract was made up to the original fifty 

 cubic centimeters with distilled water. The extracts at this stage 

 were of a rather thick syrupy consistency and a clear orange red in 

 color. To each fifty cubic centimeters then was added five c.c. of a 

 saturated solution of lead acetate, a few drops at a time, this pre- 

 cipitated the coloring matters, phlobaphenes, etc., in the extracts and 

 after standing four hours, each extract was filtered by means of a 

 suction filter. The clear straw-colored filtrates were then treated 

 with a steady stream of hydrogen sulphide gas for about ten min- 

 utes. This precipitated the lead as heavy black lead sulphide. 

 After filtering off the lead sulphide and boiling to remove any HoS 

 remaining in the extracts, the filtrates were tested, one drop of 

 cresol being added to each extract to prevent the growth of moulds. 

 As quantitive analyses were not feasible at Tortugas, colori- 

 metric methods of testing were resorted to. For the testing for 

 dextrose, Huizinga's Test was used. This is a reduction test, which 

 was found to work very well with the Rhizophora extracts. One 

 c.c. of the extract was pipetted into each of a series of test tubes and 

 diluted with five c.c. of distilled water, then one c.c. of o.i KOH 

 solution was added and one c.c. of a saturated solution of am- 

 monium molybdate was pipetted also into each tube. The tubes 

 were then boiled over an alcohol flame for 1.5 minutes and then to 



13C Bowman, H. H. M., Report on Botanical Investigation at Tortugas 

 Laboratory, Season 1916, Carnegie Inst, of Wash. Year Book, No. 15, p. 188. 



