IRANSlMKAriON AND WAri'.R SI()K\(M:. I 67 



Others there is a mass of storage tissue in a hiilh-like swelling 

 at the base of the leaf, as in Epidcndnini cochlfctliini L. and 

 l/ip(iris I'liila L., while in still others not properly belonging 

 in the same class the water is stored externally in a tank 

 formed by the inflated bases of the leaves, as in Goveuia 

 ntriciiliiia Lindl. Leaf storage of water is also common, but 

 usually occurs together with one of the other types. In Stelis 

 ()p/ii()o;l()SS()i{ii's Sw., Lepcnillics IruioilaUi Sw. and L. cou- 

 (iiiiKi Sw. the lea\'es alone serxe as storage organs. Stelis 

 was therefore found to be a con\'enient form in which to 

 study the amount and rate of water loss, with a view to 

 ascertaining how long such plants can survive without oppor- 

 tunity to absorb fresh supplies of water, and what relation 

 exists between the normal rate of transpiration and that 

 obtaining during conditions of sex'ere drought. 



Sti'lis is a plant with a small rosette of leaves which are 

 elliptical, 10 to 15 cm. long, 2.5 to 3.5 cm. wide and about 

 4 mm. in thickness. The water storing tissue occupies nearly 

 two thirds of the thickness of the leaf, lying above the 

 chlorenchma, in which there are also a few scattered cells of 

 identical appearance with the main storage cells. All of these 

 are characterised by walls which are sinuate in cross section, 

 with alternating thinner and thicker bands. The epiciermis 

 of both surfaces is very heavy, with a thick cuticle on the 

 upper and deeply sunken stomata on the lower surface only. 

 The habitat in which Slclis is most abundant is the horizontal 

 or nearly horizontal liml)S at mid-height between the floor 

 and the canopy of the forest. 



One of the determinations of transpiration rate in Sli'lis 

 was made by the potometer method, the apparatus being 

 set up in the laboratory at Cinchona where during the course 

 of the following readings the temperature varied from 67° 

 at 2 p. m. to 62 at 8 p. m. and 58 In the night, the 

 humidity from S6Y( at i p. m. and 90% from 4 to 10 p. m. 

 to 92 'r in the night. 'J'he leaf used had an area of 29 sq. 

 cm. and took up 229 mg. of water according to the total 



