114 



As regards nitrogen, soils Nos. 4 and 6 only show the amount wliich one 

 would expect from soils of this type (i.e., around 01 per cent). I'he other soils 

 are high. This is accounted for hy the large amounts of droppings from the 

 cockroaches hcfore mentioned. The screenings of Nos. 1. 2, and 3 particularly 

 had large amounts of dung, while it was less evident in Soil No. 5. This 

 "manuring" must appreciably affect the luxuriance of growth. Unfortunately, 

 no two soils taken resemble one another in all save nitrogen content, so one 

 cannot make a quantitative camparison. 



In the last colunm are given the pH values of the soils. These were deter- 

 mined colorimetrically, using Clark and Lub's series of indicators. ''■'' They bear 

 out one's expectations. The forest soil, with high humus content and exposed 

 to wind,*^^^^ is acidic, while the limestone soil is alkaline. The other granite soils 

 are also slightly on the alkaline side. This latter feature was not unexpected, 

 although granite soils, as a class, when not near the sea are slightly acidic. On 

 the island, however, the soils can all be reached by sea spray (either by dashing 

 on rocks or carried by wind), and sea water itself has a pH of about 82, due 

 mainly to magnesium and calcium salts. It is probably this fact which brings 

 the reaction from slight acidity to slight alkalinity. The possible correlation 

 between the vegetation and these values has been mentioned under "humus." 



Appendix II. 



r.iST OF specip:s collected. 



Following is a list of the species collected on Pearson Island. I am grateful 

 to Mr. J. M. Black for kindly examining my collection and determining some of 

 the plants. The Centrolepis will be described by him later. 



In addition to the name of the plant and its growth form according to 

 Kaunkaier's system, notes on the habit are given and the community in which 

 it occurs. The habit notes, leaf measurements, etc., refer to Pearson Island 

 specimens : — 



"•>) Clark, Determination of Hydrogen Ions, 1920. 

 ^'+) Warming-, Oecology of Plants, p. (i2. 



