650 BOWMAN— ECOLOGY AND 



unit increases in tannin for plants of progressively larger growth 

 vary as % of the unit increases in dextrose, i. e., the ratio is con- 

 stant and the " curve " is really a straight line. 



The result is rather contrary to the writer's expectations, since 

 on account of the extraordinary amount of tannin in the hypocotyl, 

 an agreement with the " reserve food " theory, as put forth by 

 Buignet, etc., i. e., the two substances in inverse ratio, was looked 

 for. The results, however, conform to the opposite view as ex- 

 pressed by Gerber, that is that tannin does not play a definite part 

 in the direct nutrition of the mangrove seedling. 



Before leaving the subject of tannins and physiology in general 

 it is interesting to note that in Reed's experiments,^^*^ tannic acid and 

 pyrogallol when added to cultures of wheat seedlings produced large 

 increases in transpiration. Warming^*" regards tannin as of some 

 importance in water conduction and in another place says it func- 

 tions especially as a protection against undue evaporation from 

 plants during winter, and also suggests that it may be a means of 

 rapidly restoring turgor. Regarding the function of tannin in the 

 leaves of Rhizophora, the view is here expressed for the first time, 

 so far as the writer knows, that the two layers of tannin cells in the 

 water hypodermis serve as an insulation against light and heat and 

 a protection to the water storage cells beneath it. Schimper"^ has 

 shown that the strand plants need shade and cloudy skies for their 

 best development, since the direct sunlight heats up the interior of 

 the leaves and the increased transpiration thus brought to a very 

 high degree is injurious to the plants. In conclusion it is here stated 

 then that the tannin in the leaves acts as an additional protection 

 against transpiration, and also that the tannin of the hypocotyl does 

 not contribute directly to the nourishment of the seedling. 



Ecology. 



Practical work on the ecology of the mangrove in southern 

 Florida was suggested by the work of Praeger^*- as published in the 



139 Reed, H. S., loc. cit., p. 107. 



140 Warming, Eug., loc. cit., p. 539. 



1*1 Schimper, A. F. W., " Plant Geography," 1903, p. 404. 

 142 Praeger, R. L., " Buoyancy of Seeds," Proc. Scicnt. Royal Dublin Soc, 

 rev. by E. W. Berry, Plant World, Vol. 17, No. 4, p. 131. 



