218 GROWTH OF TREES AND FORMING OF FRUIT BUDS 



conditions are satisfactory. The plants absorb from the soil, 

 through the fine root hairs, the various mineral elements. 

 These, of course, must be dissolved in the soil water before they 

 can be absorbed, and are taken into the plants through the 

 roots. Nitrogen, phosphorus, potassium, calcium, sulfur, iron, 

 and magnesium seem highly essential for most plants, but other 

 elements, including silicon, chlorine, sodium, manganese and 

 aluminum are also used. See also the reference to cases of 

 boron deficiency at the close of the chapter on managing 

 orchard soils and fertilizing the trees, page 440. 



What Elements Are Most Often Lacking in the Soil. Al- 

 though fruit trees do need and use for proper development 

 all the essential elements, experiments have shown that most 

 soils are supplied with sufficient available amounts of these 

 minerals for satisfactory tree growth and fruitfulness. Suffi- 

 cient nitrogen for best growth and fruiting, however, seems to 

 be lacking in many soils, and in such cases much better growth 

 and production result whenever it is added. 



How Trees Live and Function. In the leaves, and to a 

 small extent in other green tissue, various elaborated or di- 

 gested foods are formed. This process occurs in the presence 

 of sunlight in the green parts or chloroplasts of the leaves. 

 Carbon dioxide of the air enters through small breathing pores 

 or stomata, and is combined with water to make up certain 

 elaborated foods called carbohydrates (starches, sugars, etc.)* 



Since food and water are also combined and digested in the 

 stomach of a person, the leaves might be called the stomach 

 of the plant. With these facts in mind the great value to the 

 plant of having a large, green, and healthy leaf surface can 

 readily be seen. 



The soil foods may be considered as raw foods. After 

 being taken into the plant and combined with the carbohy- 

 drates, or other elaborated materials formed from them, they 

 help to make up certain other foods. Of these foods, the carbo- 

 hydrates and proteins are very important. The carbohydrates, 

 proteins, and other materials derived from them are formed 



