2 The Philippine Journal of Science 1914 



Bulacan, and Bataan Provinces and in parts of others; for 

 example, Zambales, Cavite, and Batangas, the dry season is very 

 pronounced. 



The humidity which regulates plant transpiration is only 

 second in importance to rainfall. There is not the same marked 

 variation in the mean humidity of the eastern and western 

 zones as in the rainfall, but a close association of the two factors 

 is evident. 



All the conditions which influence the soil must be taken into 

 account, for any one may become a controlling factor in the 

 production and quality of crops. Climatic and physical con- 

 ditions are as important as the chemistry of the mineral matter. 

 A discussion of the influence of rainfall ; humidity ; mean, maxi- 

 mum, and minimum temperatures; the temperature under the 

 surface of the ground ; the amount of light and sunshine ; winds 

 and evaporation of the soil moisture; exposure; altitude; etc. 

 on the soil has already been given in a paper on Philippine 

 soils and some of the factors which influence them.^ There is 

 so little variation in most of the climatic factors in the Philip- 

 pines that, in the comparison of one region with another, prac- 

 tically all of them, except rainfall, drop out of consideration. 

 Alternations of wet and dry periods often show marked dif- 

 ferences in vegetation, and frequently the prevalence of any 

 particular type is directly correlated with the rainfall. It is 

 remarkable how certain crops; such as, coconuts, hemp, and 

 tobacco, which depend upon a rainfall well distributed through- 

 out the year, not only are restricted to the eastern rain zone 

 but completely coincide with it.= 



The mineral constituents of a soil may indicate high fertility, 

 but the physical components (the amount of humus * and un- 

 humified organic matter and the size and shape of the inorganic 

 grains) may be such as to counteract this. The agricultural 

 value of soils is determined not only by chemical composition 

 and climatic and local conditions, but also in many cases by 

 their physical character. There are instances of soils identical 

 in every respect, except with regard to physical texture, which 

 show a marked difference in crops. Some crops are most 

 economically gi'own and thrive best in loose mellow soil, while 

 others require "heavy" soil with strong retentive power for 

 moisture. 



'Cox, Alvin J., This Journal, Sec. A (1911), 6, 281, et aeq. 



'Cox, loc. cit., 300. 



'The complex organic product of decomposition. 



