60 A MONTANE RAIN-FOREST. 



extremely hygrophilous ferns of the narrowest Windward Ravines. 

 The five herbaceous species last named were chosen as being the most 

 characteristic plants of the three habitats of the rain-forest which 

 differ most pronouncedly in general moisture conditions, as well as 

 being suited to the requirements of experimentation. 



In work with Alchornea, Clethra, and Dodoncea only cut shoots were 

 used, and the potometer method was required for measurement of their 

 transpiration. The greater part of the work was done with potted 

 plants of the herbaceous species, and by the method of weighing sealed 

 pots. The material used in 1909 was potted two months in advance 

 of my arrival at Cinchona, and kept in the shade of a row of bamboos, 

 I was thereby supplied with a set of vigourous plants in normal condition. 



Nearly all of my experimentation was carried on in the physiological 

 laboratory building of the Tropical Station at Cinchona, which is 

 admirably suited for such a purpose. This building is about 12 by 24 

 feet in size, provided with a deep wall table, above which the sides of 

 the building are completely occupied with alternating glass windows 

 and open windows provided with jalousies. The light conditions are 

 practically like those of the floor of the forest, and the temperature 

 and humidity follow the outdoor shade conditions of the Leeward 

 Slope both quickly and closely. Plants subjected to continuous dark- 

 ness were placed in a small closet under the wall table, which was made 

 light-tight by using a double jacket of plant driers. The arrangement 

 of the jackets was such as to provide ventilation, and the size of the 

 closet was great enough to enable me to get inside it and thereby to 

 assure myself of its darkness. A moist closet was used, which was 

 made of window sash and placed next to one of the windows of the 

 laboratory. Portions of its sides were covered with plant driers, kept 

 constantly wet, and its floor was covered with sphagnum moss. It 

 was possible to keep the humidity of this closet between 90 and 95 

 per cent without difficulty. 



The woody shoots used in transpiration experiments were in each 

 case cut under water and allowed to stand in water from six to ten 

 hours before use. The potted plants were prepared for use by covering 

 the pots with plastocene, over which was rubbed a thin coating of 

 vaseline. The pots were not sealed at the bottom, but were placed 

 in saucers for convenience in handling. A water-tight joint was then 

 made around the circumference of the base (see plate 21 B). This 

 made it possible to use a potted plant a second time by removing it 

 from the saucer, taking off the cardboard top (covered with plastocene), 

 and giving it a "rest" of several days. 



The moisture of the soil in which my potted plants were growing 

 was not precisely determined in connection with the transpiration 

 series in which they were run. The soil used had been made up in 

 such a way as to be uniform for all the pots, and each group of pots 



