262 



3. Calculation of Leaf Areas. 



To express the transpiration rate in terms of the weight of water transpired 

 per sq. cm. per hour it is necessary to determine the total transpiring area. 

 This was a tedious matter, as it necessitated the computing of several hundreds 

 of leaves. In the case of Airiplex and Rhagodia the leaf outlines were traced 

 on paper, cut out, weighed, and compared with the weight of a known area of 

 the paper, and from this the area was calculated. Casuarina, Pholidia, and 

 Kochia were treated as cylinders, the total length being measured, and also the 

 diameter, the latter by means of an objective micrometer. In the case of 

 Pholidia, the areas of leaves of stem were calculated separately. The leaves of 

 Geijera were treated as rectangles. All the flat leaves had stomates on both 

 sides ; the areas obtained by the above methods were therefore doubled in these 

 cases. 



The number of leaves and the total transpiring areas of the shoots were as 

 follows : — 





Number of 



Total Transpiring 



Plant. 



Leaves. 



Area (sq. cms.). 



Casuarina lepidophloia 



71 



392-4 



Geijera parviflora 



. 154 



4591 



Pholidia scoparia 



. 155 



1981 



Atriplex vesicarium 



. 258 



4461 



Rhagodia GaudicJiaudiana 



. 330 



6906 



Kochia sedifolia 



. 2,800 



7147 



RESULTS. 







Fig. 2 is a table embodying the results obtained. Transpiration is 

 given by the figure opposite each species of plant and represents the loss of 

 water in milligrams per sq. cm. The atmometer readings are reduced also to 

 the loss in milligrams per sq. cm. The light intensity is given in seconds, the 

 relative humidity in percentages, and the temperature in degrees F. 



No readings were taken between 11 p.m. and 7 a.m. next morning. The 

 small amount of water transpired during this period is shown below. Assuming 

 that the transpiration rates were constant during this period the hourly losses 

 were : — 



Atriplex vesicarium . . . . . . . . . . 09 mg. 



Rhagodia GaudicJiaudiana 

 Kochia sedifolia 

 Geijera parviflora 

 Pholidia scoparia 

 Casuarina stricta 

 Atmometer 



07 mg. 



07 mg. 



08 mg. 

 10 mg. 



TO mg. 

 ■70 mg. 



