69 



this paper hold out definite hope of the financial possibility of the 

 treatment of small isolated areas and offer some hope even of 

 the possibility of applying- such treatment to large areas. 



(c) PLANT PATHOLOGY. 



LVIII. Wm. B. Brierley. " The Relation of Plant Patho- 

 logy to Genetics." Report of Imperial Conference of 

 Botany, London, 1924. (Cambridge University Press.) 

 pp. 111-119. 

 A critical discussion of the problem. Where disease is due 

 to growth in unfavourable conditions the problem resolves itself 

 into a study of the g-enetical qualities of the plant in relation to 

 soil, climate, etc. Where disease is brought about by parasites 

 a complete understanding of any particular case involves the 

 genetic and physiological analysis of both host and parasites and 

 the physical and chemical analysis of the conditions under which 

 the host and parasites have developed and at present exist. 

 Assumption of germinal stability by the plant breeder and of 

 germinal instability by the microbiologist are antithetic and 

 require deeper analysis. Immunity and susceptibility relation- 

 ships are often confined to pure lines of host and physiological 

 strains of parasites and alterations in external conditions may 

 greatly modify the phenotypic expression of this relationship. 

 The primary factors that determine the appearance of disease 

 in any particular case are (1) the genetic qualities of host and 

 parasite; (2) environmental conditions; (3) relative geographic 

 distribution of host and parasite. An additional factor of import- 

 ance is the relation of the hygiene of the host to the incidence of 

 disease, the commonly held ideas on which are urgently in need 

 of revision. Most of the past analytic work on the genetics of 

 micro-organisms and the disease relationship needs revising in the 

 light of the following : (a) the co-existence of distinct physio- 

 logical strains in morphological units ; (b) the possibility, and in 

 certain cases probability, of very considerable genetic complexity 

 and genetic segregation in micro-organisms. Genetic research 

 on bacteria and fungi is incommensurable with that on the more 

 evolved organisms which is the basis of present genetical theory 

 and in the study of the former exact criteria and definite concepts 

 are almost entirely lacking. 



TECHNICAL PAPERS. 



(a) SOILS AND FERTILISERS. 

 LIX. H. J. Page. " The Chemistry of the Soil and of 

 Crop Production," in " Chemistry in the XXth 

 Century." (Benn Bros., 1924.) pp. 225-242. 

 Following a foreword by Sir John Russell, the subject is 

 discussed with special reference to the progress made since 1900, 

 more particularly by British workers. 



LX. B. A. Keen. " Soil Tilth in Relation to Mechanical 

 Tillage." Agricultural Gazette, 1924. Vol. C, pp. 

 297-298. 

 An account of the work on soil cultivation being done in the 

 Physical Department. (See p. 28.) 



