IMPROVING QUALITIES 



495 



5925 



365. Making the most of our plants. Having selected the best 

 seeds or the best types, the next problem is to make the most 

 of each crop. We know that plants are influenced by the physi- 

 cal conditions in which they live, so that we are able, to a 

 certain extent, to control 

 their behavior. 



I. Soil. The soil must 

 have a texture that will 

 permit both air and water 

 to penetrate to the roots, 

 and at the same time the 

 surface must not allow the 

 water from below to evap- 

 orate too rapidly. To in- 

 sure the right physical 

 condition the soil is culti- 

 vated—plowed to bring up 

 the deeper layers and to 

 break up the packed earth, 

 and harrowed to crumble 

 the lumps further into 

 loose particles. If there is 

 too much clay, sand has 

 to be added: if it is too 

 sour, lime has to be added ; 

 and, in general, fertiUzer 

 of one kind or another is 

 mixed into the earth to 

 supply ingredients needed 

 for the particular crop or 

 to supply deficiencies in 

 the particular soil. Since 

 some plants depend upon the cooperation of particular species 

 of bacteria in making use of atmospheric nitrogen, modern 

 farm practice has often added cultures of such bacteria to the 

 prepared soil. 



12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 



Fig. 



209. 



V^ariation in physiological 

 properties 



Forty thousand sugar beets, tested individu- 

 ally, showed from 12 per cent to 19 per cent 

 of sugar. Beets containing 15.5 per cent of 

 sugar were the most frequent, but there were 

 almost as many beets with 15 percent or with 

 16 per cent. As the percentage of sugar de- 

 parts more from the t.vpical 15.5 per cent, the 

 number of individuals with a given sugar con- 

 tent diminishes, so that the extremely poor 

 and the extremely rich beets are also fewest 

 in number 



