IV.] QUALITY IN PRODUCE 77 



season, etc — are comparatively small as measured bj' 

 such rough analytical factors as the percentage of 

 nitrogen, etc., they are often of extreme importance 

 commercially, because they may and generally do affect 

 those more subtle items in the composition of the 

 product summed up as quality. We are as yet rarely 

 in a position to define from a chemical standpoint what 

 constitutes quality in each particular case, still less to 

 state the external factors which determine it ; we may, 

 however, be sure that it is not due to the mere presence 

 or absence of some particular ingredient in the soil. 

 We have seen that all plants are fundamentally made 

 up of exactly the same things in very similar propor- 

 tions, the differences arise in the style of the architecture 

 that the plant adopts in each case ; and if wheat is 

 " stronger " when grown in one place than another, it is 

 not because in the soil of the first place there exists 

 some element which is absent in the soil of the second 

 place, but because the habits of the plant are affected 

 variously by differences in the supply of water, air, or 

 warmth in the two places. We have, in fact, many 

 reasons for regarding the supply of water and the 

 prevailing temperature as the main factors in determin- 

 ing both the yield and the quality of all crops, and it is 

 from this point of view that it is most profitable to 

 regard the soil 



