44 Report op the Acting Director and Chemist of the 



All plants can not use nitrogen in any of these three forms equally 

 well, but each form is found specially suited to certain kinds of 

 plants as will be noticed.- 



(1) Nitrogen Gas used by Plants. — Although we have nitrogen 

 gas or uncombined nitrogen existing in the air in enormous quantities, 

 still the number and kinds of plants which can use the nitrogen of 

 the air is not large. In general, those plants which are called 

 leguminous, such as the bean, pea, clover, alfalfa, etc., can take un- 

 combined nitrogen from the air. Upon the roots of such crops are 

 found certain lumps or warts or tubercles. These tubercles contain 

 large numbers of micro-organisms derived from the soil and these 

 micro-organisms have the power of bringing the nitrogen of the air 

 into such combinations as the plant can use. 



(2) Nitrogen of Ammonia used by Plants. — The leaves of 

 some plants have the power of absorbing ammonia directly from 

 the air and obtain nitrogen in this way, but only in very small quan- 

 tities. Some plants obtain nitrogen from ammonium salts through 

 the soil, but in general, the compounds of ammonia are changed into, 

 nitrates in the soil before being used by plants. 



(3) Nitrogen of Nitrates used by Plants. — The largest 

 part of the nitrogen obtained by most plants is taken up by their 

 roots from the soil m the form of nitrates ; that is, nitric acid com- 

 bined with some metal, as sodium or potassium. As already stated, 

 most of the nitrates used by plants are formed by changing into 

 nitrates ammonia compounds and organic substances in the soil by 

 the process called nitrification. Hence, nitrogen^ in the form of 

 nitrates, is the most a^ailaUe form for most plants ; that is, it can 

 be most readily taken up and used by plants. 



Phosphorus. — {a) Description. — Phosphorus, when uncom- 

 bined with other elements, is a yellowish, waxy-looking, solid sub- 

 stance. It is soft and can be cut as easily as ordinary beeswax. It 

 is very poisonous. It takes fire very easily and, therefore, has to 

 be kept under water. When phosphorus burns, it simply unites 

 with the oxygen of the air, forming a compound which contains 

 oxygen and phosphorus ; this compound of oxygen and phosphorus 

 is commonly called phosphoric acid. 



(b) Occurrence. — Phosphorus is always found in nature com- 

 bined with other elements. It 03curs combined with oxygen and 

 calcium (or lime) and this compound is called calcium phosphate or 

 phosphate of lime. It also occurs in soils as phosphate of magnesia,, 



