259 



ON TRANSPIRATION IN THE FIELD OF SOME PLANTS FROM THE 

 ARID PORTIONS OF SOUTH AUSTRALIA, WITH NOTES ON THEIR 

 PHYSIOLOGICAL ANATOMY. 



By J. G. WooD^ B.Sc, Demonstrator in Botany, University of Adelaide. 



[Read September 13, 1923.] ; 



Plate XXI. 



The Australian flora presents a great range of variation in form and some 

 remarkable structural features arising from the arid conditions. There has been 

 a surprising neglect of quantitative experimental work attempting to correlate 

 these modifications with the physiological processes of the plants. Ewart (1910) 

 determined the transpiration rates of three species of Eucalyptus (E. viminalis, 

 E. corynocalyx, and E. maculata) , but the work was mainly concerned with the 

 problem of the ascent of the sap. More recently Cannon (1921) has described 

 the anatomy of several species of plants from the arid portions of South 

 Australia in relation to various ecological factors, chiefly the problem of the 

 water supply. 



The following paper first describes the transpiration rates of six species of 

 plants in relation to various external factors, and, secondly, attempts to correlate 

 the transpiration rates with the histological modifications which are developed 

 in the transpiring organs. 



I. TRANSPIRATION. 



Physical Environment. — The experiments were carried out in the field at 

 Dilkera, a sheep station about 10 miles north of Mount Mary, a small township 

 on the Morgan railway line, and 90 miles north-east of Adelaide. Dilkera is in 

 the Murray basin, and has an average annual rainfall of 928 inches (Morgan). 

 A visit was made during the third week of May of this year ; this was towards 

 the end of a period of about five months' drought, and the weather was typical 

 of autumn conditions in this region. At this period of the year the country is 

 subject to strong westerly and south-westerly winds, which sweep over the plains 

 from the Mount Lofty Ranges. These winds are dry and often travel at a high 

 velocity. As will be shown below, they are an important factor in determining 

 the rate of transpiration. 



As regards vegetation, the chief communities are an open woodland of 

 Casuarina lepidophloia or various malices (Eucalyptus spp.), in conjunction with 

 undershrubs, the chief being Atriplex vesicarium and Kochia sedifolia. The 

 transpiration experiments were carried out under as natural conditions as pos- 

 sible. The situation is shown in pi. xxi., fig 2. The chief shrub is the "blue- 

 bush," Kochia sedifolia, with remains of bushes of Atriplex vesicarium, though 

 most of the latter have been eaten out by grazing animals. The trees are 

 Casuarina lepidophloia and Myoporiiin platycarpmn. The apparatus was fully 

 exposed to all climatic factors and only protected from grazing animals by a 

 single barbed-wire enclosure. 



The plants selected for experimentation were Casuarina lepidophloia 

 (F. V. M.), Geijera parviflora (Lind.), Pholidia scoparia (R. Br.), Atriplex 

 vesicarium (Hew.), Kochia sedifolia (F. v. M.), and Rhagodia Gaudi- 

 chaudiana (Moq.). 



