644 BOWMAN— ECOLOGY AND 



Laguncularia raccmosa have broadened the knowledge of these 

 organs. 



Before leaving this subject of transpiration, mention may be 

 made here of some potometric measurements. At the Tortugas 

 Laboratory a few potometer records were taken with shoots of 

 Rhicophora to form some actual quantitative estimate of the water 

 transpired through the leaves. Shoots of an average weight of 3.2 

 grams were used and the same conditions of humidity, light inten- 

 sity and temperature were arranged as for the transpiration records 

 above mentioned. It was learned that the average transpiration of 

 these shoots was approximately one cubic centimeter in thirteen and 

 four tenths minutes. This data, however, has no direct relation to 

 the data of the bulk of the experiments performed. 



Biochemical Experiments and Tests. 



As mentioned in the prefatory statement attached to this paper, 

 certain biochemical investigations were carried on at the Tortugas 

 Laboratory on the cellular contents of the Rhicophora seedlings, the 

 two substances being dextrose and tannic acid. The purpose in 

 undertaking the investigation was to gain some idea, if possible, of 

 the role played by the tannin in the physiology of the mangrove, 

 since this occurs in such large amounts in the plant's tissues. Sev- 

 eral authors have suggested the various functions played by tannin 

 in the plant's economy ; Wiesner, for instance, believed that tannin 

 is an intermediate product in the formation of resin, since it has 

 been observed that in Pimis, as the tannin decreases in the spring, 

 i. e., during the season that the resin is most abundant, there is a 

 corresponding increase in the resin. Basset^"'- has suggested that 

 the tannin content of fruits more particularly depends on certain 

 enzymes. Buignet,^-'' in his work on the banana, argues that from 

 the diminution of starch and tannin as the truit ripens, there is 

 ground for supposing that tannin assists in the formation of sugar. 

 On the other hand, Gerber^-' in his studies on the relation of the 



125 Basset, B., Ref. Haas and Hill, 131. 



126 Buignet, A., Ann. de chcvi. et de Phys., III., Ser. I., LXL, p. 281, 1861. 

 12" Gerbcr, C, Ann. de Sci. Nat., IV., 1897, pp. 1-280. 



