CHAPTER II 

 WHAT PLANTS NEED 



6. General statement. Such plants as we cultivate may 

 be thought of as living machines that manufacture food, that 

 grow, and that finally store food. In general, it is on account 

 of the stored food that they are cultivated. If the manu- 

 facture of food is to be carried on efficiently, there must be 

 favorable conditions and available materials. It is necessary 

 to discover what these are, and also whether we can be of 

 assistance in supplying them. 



What may be spoken of as the conspicuous conditions for 

 successful plant work are oxygen, light, and heat. The 

 practical question is, therefore, how can we assist plants in 

 securing these conditions ? 



7. Oxygen. In reference to the oxygen supply obtained 

 from the air, it is evident that it is abundant for the parts 

 above ground wherever plants are cultivated. But there 

 are living and working parts of the plant imbedded in the 

 soil, and most plants are started by seeds buried in the soil, 

 and here the problem of a free oxygen supply calls for our 

 help. If the spaces within the soil are filled with water, the 

 air is excluded ; if the soil is packed too firmly, the air can- 

 not circulate ; or if there is too much clay in the soil, the air 

 is not free to move. All such conditions must be remedied 

 if plants are to grow well. The water must be drained off ; 

 the soil must be loosened up ; the impervious clay must be 

 mixed with something that will give a looser texture to the 

 soil. One of the most common blunders in planting seeds 

 when artificial watering is employed is to use too much water, 

 so that the seeds are in a " puddle " and the air is excluded. 



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