Nov., 1918] Recovery of Vegetation at Kodiak 13 



cases above the average of those produced before the eruptions, 

 were obtained without the addition of manure; but only for 

 one, and sometimes two years. That this temporary increase 

 in fertihty was not entirely due to deep cultivation is evident 

 by the fact that only the upper 3 or 4 inches of the old soil were 

 touched in the process, and that it is now necessary to manure 

 heavily to obtain average crops. " The cause of this temporary 

 increase in fertility is believed to be due, not to "any available 

 food materials in the ash or to any improvement in the physical 

 condition of the soil, " but to the effect of the partial sterilization 

 of the soil by the heat of the ejecta, which increases the quantity 

 of available nitrogen compounds because of the increase of 

 bacteria consequent upon the destruction, by the heat, of the 

 larger organisms that prey upon them, as has been found to be 

 the case by Russel and Hutchinson at Rothamsted. 



This explanation of the temporary increase of fertility by 

 the ejecta is very interesting as, perhaps, in a measure accounting 

 for the widespread idea that volcanic ash has value as a fertilizer. 

 Although the ash from Katmai was not hot as it fell, there was 

 some suggestion at Kodiak and elsewhere of a similar stimulating 

 effect of the ash fall. 



TARAWERA. 



Among the notable eruptions of the last fifty years was that 

 of Tarawera in 1888. This has been discussed recently in an 

 excellent paper by Aston. ^^ The following quotations will serve 

 to summarize his conclusions: 



"Occasionally, where the water-supply is favorable, lichens 

 and moss may perform their usual function of transforming 

 the barren rock into fertile soil, but the Raoulia must be 

 accounted the great humus maker of this mountain. As it 

 languishes in vigor, owing to age, from it grow other plants, the 

 chief woody ones being Coriaria and Leptospernum, and 

 sometimes Pittosporum, but also herbaceous plants such as 

 Trifolium and Rumex acetosella. Four stages may thus be 

 predicted for the repeopling of the plant-covering of this open 

 area (excluding the ravines, which are able to jump the first 



" Aston, B. C. The Vegetation of the Tarawera Mountains, New Zealand. 

 Trans. N. Z. Inst. 48: 304-314. 1916. The same paper is published with minor 

 changes in the text and somewhat different iUustrations in the Journal of Ecolog}-. 

 4: 18-26. 1917. 



