Colonisation of bare Ground 51 



waves produced during storms constantly wash up on to the beach 

 large quantities of organic material, sea-weeds and marine animals, so 

 that a plentifully supplied nidus would always be found at a distance of 

 50 metres or more from the coast ; from this the underlying porous 

 pumice and ashes would derive organic and inorganic products of 

 decay. 



As regards the establishment of conditions favourable for plant- 

 life in the interior of the island, other sources must be considered ; 

 clouds of dust blown by local winds from the shore ; minute particles 

 of inorganic and organic substances brought by the monsoon together 

 with micro-organisms and the spores of mosses and ferns; also the 

 seeds of phanerogamous plants ; and lastly, the nitric and nitrous acids, 

 which constitute the chief supply of nitrogenous food, provided by rain. 

 We are justified in assuming that in equatorial regions the oxidation 

 of nitrogen to nitrates and nitrous acid takes place under the in- 

 fluence of electrical discharges, which accompany the almost daily 

 storms, at least with as much activity if not with much greater 

 activity than with us. 



Despite the comparatively small amount 1 of nitrogenous material 

 which is added to the ground by rain in a single year, it would 

 however be sufficient, together with the salts and traces of organic 

 matter contained in the ash, to support even in the first years after 

 the eruption a rich flora of micro-organisms. 



Three years after the volcanic outburst dark green gelatinous 

 layers of "blue-green" algae were found on the surface of the pumice 

 and ash and on the loose stones in the ravines of the mountain 

 slopes ; these were correctly regarded by Treub as affording a 

 satisfactory nutritive medium for the germination of the spores of 

 cryptogams and the seeds of phanerogams. The important part 

 played by algae, particularly the Cyanophyceae, in the colonisation 

 of bare ground and poor soil has since been demonstrated in many 

 other localities, and recently Fritsch 2 has dealt fully with this subject 

 also in the case of tropical regions, especially in Ceylon. 



The Bacteria and Mould-Fungi may perhaps have played even 

 a more important part in the'preparation of a favourable substratum 

 for the higher plants in the earliest phase of colonisation. Researches 

 into the Bacterial flora were first undertaken during our (the third) 



1 In Europe according to Boussiugault there are 1 6 milligrammes of nitric acid 

 in a litre of rain-water; Von Ad. Mayer calculates that in a year the rain brings down 

 about 1 kilogramme to each hectare [2 - 47 acres]. 



2 Fritsch, F. E. " The role of Algal Growth in the Colonisation of new ground 

 and in the determination of Scenery." The Geographical Journal, November 1907, 

 pp. 531-548. 



42 



