DEPARTMENT OF MARINE BIOLOGY. 



189 



As intimated above, equal weights of the selected hypocotyls were taken 

 and ground up in a mortar, extracted with distilled water, and the extract 

 filtered. These extracts were made both by infusion and decoction, in 

 different instances, but the resulting differences in strength were negligible. 

 The filtered extracts were treated with certain reagents and tested for tannic 

 acid and dextrose by colorimetric methods. Quantitative methods were 

 not feasible at the laboratory, so after trying many special tests and reagents, 

 Hager's test for tannic acid and Huizinga's test for glucose were decided 

 upon as the most practicable under the peculiar conditions obtaining and 

 with the available supply of material. The details of these tests and the 

 technique used in handling this mangrove material will be given in a subse- 

 quent paper. In all, over 90 tests were made in the few weeks devoted to 

 this portion of the season's work, including the preliminary experiments in 

 working out the best method in dealing with the material. Control solu- 

 tions of varying strengths were 

 made up afresh for each series of 

 tests, both of Merck's standard 

 tannic acid and Kahlbaum's stan- 

 dard dextrose. In checking up the 

 results of the tests, arbitrary stan- 

 dards of extract were made by com- 

 parison with the control solutions of 

 known percentage content. These 

 standards were of six grades, each 

 approximating a certain percentage 

 of tannic acid or dextrose. 



I once thought there might be 

 some definite relation between the 

 amounts of the substances in the 

 hypocotyls of different ages and 

 with different growth conditions — 

 for instance, that with increasing 

 growth the tannic-acid content of 

 a hypocotyl might decrease, with 

 perhaps a corresponding increase 

 in the sugar content. In the light 

 of these preliminary tests, this 

 does not seem to be the case, but 

 with increasing growth and expansion of the protosynthetic tissues in the older 

 seedlings and the transformation of the starch stored in the hypocotyl, the 

 sugar increases in a steady upward curve. In the case of the tannic acid, 

 however, such is not the case; there is a decrease in this substance in the 

 young seedling just pushing out roots and unfolding the plumule, then with 

 later growth and greater synthetic activity there is a slight regular increase in 

 tannic acid. The behavior of this curve can not be explained just yet, although 

 the author hopes to give the Ijiological interpretation of this fact when the 

 data have been worked out to a fuller degree and a larger series of experiments 

 made on this particular phase of the problem with better controlled conditions 

 for the sprouting hypocotyls. A condensed graph of the tendency of variation 

 in the amounts of dextrose and tannic acid in Rhizophora hypocotyls is given 

 herewith. While these experiments were being conducted on the dextrose and 

 tannin contents, a series of tests were made to determine the presence of the 

 enzyme, tannase in the hypocotyl of Rhizophora. Definite weights of selected 



