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THE FLORA AND FAUNA OF NUYTS ARCHIPELAGO AND THE 



INVESTIGATOR GROUP. 



No. 8.— THE ECOLOGY OF PEARSON ISLANDS. 



By T. G. B. OsBORN, D.Sc, Professor of Botany in the University of Adelaide, 



with an Appendix on the Soils, 



By J. G. Wood, B.Sc, Demonstrator in Botany. 



[Read April 12, 1923.] 



Plates IV. to IX. 



The following account of the ecology of Pearson Islands is based on observa- 

 tions made during a stay on North Pearson from January 5 to 12 of this year. 

 I desire to express my thanks to Prof. F. Wood Jones, leader of the party, for 

 assistance in various ways, and to Mr. T. D. Campbell, for permission to make 

 use of his sketch map of the islands in constructing text fig. 1. 



The party is indebted to Sir G. J. R. Murray, K.C.M.G., for a genei-ous 

 donation towards the cost of the expedition. 



Pearson Islands lie in lat. 33° 58' S.. long. 134° 15' E.. at a distance of about 

 40 miles from the nearest mainland, the west coast of Eyre Peninsula, South 

 Australia. They are, however, only 18 miles south-west from Flinders Island, 

 a comparatively large island, the area of which is 9,000 acres. They are the 

 south-western islands of the Investigator group, and were named by Matthew 

 Flinders in 1802, but were not visited by him. Robert Brown, who was naturalist 

 on board H.M.S. "Investigator," did not. therefore, land upon them, and, as the 

 islands are uninhabited, with a rather uncertain landing, it is improbable that 

 they have been visited by a botanist before. 



According to the Australia Directory"* the Pearson group consists of four 

 islands and a rock partly above water. This paper refers only to the North 

 Island of the Directory, which is the largest and most important. No landing 

 could be made on any of the other islands. Two of them are too precipitous for 

 any landing, though one might be effected upon the third. A careful examination 

 of the vegetation upon them by means of field glasses indicates that the flora 

 is of the same type as on the more exposed parts of North Island. These out- 

 lying islands will not be referred to again in this account. 



PHYSIOGRAPHIC FEATURES. 

 The North Island of the Australia Directory consists of two, or, for descrip- 

 tive purposes, preferably three land masses lying close together (text fig. I). The 

 southern land mass is connected with the middle one by an isthmus of bare granite 

 bovilders, which is above high-tide mark, but would in storms be entirely spray 

 drenched. The northern land mass, which is the largest, being about H miles 

 long by H miles broad, is separated from the middle one by a strait about 100 

 yards across, and can only be reached by wading at low tide in calm weather. 

 In the following account the North Island of the Australia Directory will be 

 spoken of as if it were three separate islands, called respectively Northern, 

 Middle, and Southern. The group consists of exceedingly bold, rugged, granite 

 islands rising in one place on Northern Island 781 f eet /^'^ above sea level. The 



(1) Australia Directory, 10th Edition, p. 169, 1907. 



(-) The altitudes are taken from the Hydrographic Survey, Australia Directory, loc' cit. 

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