H. B. Hutchinson and K. MacLennan 103 



This gradation appears to apply quite generally to the soils on this 

 formation (clay with flints, overlying chalk), but need not necessarily 

 mean that on other and diflierent soils the above plants are associated 

 with the acidities^ already given. There seems to be httle doubt from 

 general observation that clovers are least and sorrel most acid-resistant 

 (neglecting the terms calciphagous and calcifugous), but the extent 

 to which these various plants persist on any given soil is probably 

 determined partly by reaction and the amount of water contained by 

 that soil at any period. In this connection organic matter by helping 

 to retain soil water might conceivably play a part in regulating these 

 inter-relations, which go to form a subject of agricultural importance 

 and of ecological interest. 



Summary. 



The experimental results described in the two parts of the paper 

 may be summarised thus : 



Part I. Li)iie Requirements for Sterilisation Purposes. 



(1) The capacity to produce partial sterilisation effects is a property 

 belonging to calcium oxide (caustic lime), but not to calcium carbonate 

 (chalk, limestone, marl, etc.). 



(2) The amount of Hme necessary to produce specific effects in 

 different soils has been found to vary greatly and it is not possible to 

 make any general recommendations. 



(3) The method proposed for indicating the critical amount 

 required is based on the determination of the amount necessary for 

 the production of an alkaline reaction of the soil water. 



(4) The amounts thus indicated agree very closely with those 

 required for the production of typical partial sterihsation eiiects in 

 the soil itself, e.g., the inhibition of protozoa and of nitrifying organisms, 



(5) By correlation of the results obtained by the proposed method 

 with those of pot experiments, it is evident that the amount indicated 

 coincides with that required for (a) the maximum production of dry 

 matter in the first crop following treatment — heavier apphcations 

 tending to be injurious, and (6) the maximum production of dry 

 matter in the first /owr crops. Apphcations of lime double or treble the 

 amount indicated by the method, although causing an increase in the 



' The types of "soil acidity" or lime requirement vary greatly and require further 

 study in their relation to plant growth. 



