208 Bureau of Farmers' Institutes. 



by plants in order to produce the proteids and many of the vegeta- 

 ble oils and characteristic flavors, such as those contained in horse- 

 radish, mustard, turnips, onions, etc. 



Iron. 



\(a) Source. — Iron in various forms of combination is a con- 

 stituent of all agricultural soils. 



(b) Relation to Fertilizers. — As a rule, iron compounds rarely 

 need to be supplied to plants by artificial application, because they 

 are used only in minute quantities by plants, and agricultural soils 

 contain abundant quantities. However, though used only in very 

 small amounts by plants, iron compounds are absolutely essential 

 to satisfactory plant growth. 



(c) Specific Functions in Plant Growth. — Iron compounds are 

 necessary for the production of chlorophyll in plants. Without, 

 iron compounds in the plant no chlorophyll is formed; without 

 chlorophyll, there will be no formation of starch and little vege- 

 tative activity of a normal character. 



Chlorine. 



(a) Source. — Uncombined chlorine is never found in nature. 

 We commonly know chlorine only in its compounds. Chlorine 

 combined with hydrogen forms hydrochloric or muriatic acid. 

 Chlorine combined with any metal forms chlorides commonly 

 known also as muriates. For example, chlorine combined with the 

 metal sodium forms a compound which is called sodium chloride or 

 chloride of sodium, or muriate of soda ; and this sodium chloride 

 is the common salt familiar to us in every day experience. Chlo- 

 rine combined with the metal potassium forms potassium chloride 

 commonly called muriate of potash. 



(6) Description.- — Chlorine, when not combined with other 

 elements, is a greenish-yellow gas, having a very suffocating odor. 

 The gas is very poisonous and has very active chemical power. 



(c) Relation to Fertilizers. — While chlorine is known to be 

 an essential constituent of plant food, at least with many or most 

 plants, the circumstances which require its addition to the soil ap- 

 pear extremely rare, except in some cases where it may be used 

 for an indirect benefit. It is added to fertilizers in considerable 

 quantities in the form of potassium chloride (muriate of potash) 

 but this is largely because this happens to be the cheapest form in 

 which potash can usually be obtained. It is the effect of the potash, 



