116 PLANT FOODS AND PLANT GROWTH 



Grape sugar which is formed in the green parts of plants 

 can be readily transformed into starch by the loss of one molecule 

 of water (C 6 H 12 O 6 H 2 O = C 6 H 10 O 5 ). In some plants, 

 such as the sugar beet and sugar corn, the sugar is transferred 

 directly and stored as such without change. But in most plants 

 it is very quickly transformed into starch, which is reconverted 

 into sugar during the night and transferred to other parts. 

 Therefore, if the leaves are examined early in the afternoon they 

 will be found to' be very rich in starch as compared with their 

 condition before sunrise. 



Other Organic Compounds Formed. We know that search 

 and sugars are the most abundant food products of the plant; 

 that they are especially abundant in vegetables, fruits and seeds. 

 But we also know that there are other substances, such as hydro- 

 carbons (fats and oils) ; and the proteins, which contain nitro- 

 gen (and some sulphur and phosphorus). These are among the 

 most important food products, but we know very little about 

 their formation. 



Mineral Substances. Plants take a great many minerals 

 from the soil. The most important are phosphorus, potassium, 

 calcium, magnesium, sulphur, iron, sodium, chlorine, silicon, 

 manganese and aluminum. These elements go into solution in 

 the water of the soil and then pass into the root-hairs in the 

 manner already described. They may be found by making 

 a chemical analysis of the ash of the plant. They vary in pro- 

 portion in different species of plants, in plants at different ages 

 and in different parts of the same plant. 



These minerals exist in varying quantities in the soil, but 

 their proportions may not be such as are .needed by the crop, 

 or they may not be in such form as to be available as plant food. 

 Therefore, the progressive farmer, who is familiar with his 

 soil and with the needs of his crop, makes use of manures 

 and commercial fertilizers to overcome these deficiencies. 



Nitrogen and Protein. One other most important element 



