1879.] THE GARDENER'S PRIMER. 137 



Other of the elements are of the metallic class, such as calcium, 

 in its carbonate state as limestone constituting vast mountains, and as 

 chalk, enormous beds, which are decomposed by the action of the 

 atmosphere and by rain-water, which, by-the-by, contains carbon 

 dioxide (carbonic acid) : this limestone or chalk when burnt in a 

 kiln becomes calcium monoxide or quick lime. Aluminium in the 

 state of an oxide of aluminium is clay, which is felspar weathered or 

 exposed to the action of the atmosphere until disintegrated, and 

 felspar is a double silicate of aluminium and potassium. Other 

 of the elements are magnesium, potassium, and sodium, the two 

 latter not identical in their operation, the one not supplying the place 

 of the other in plant structure ; and in combination with oxygen are 

 the alkalis potassa and soda. The former (potassium) enters largely 

 into the composition of land plants as a chloride, and is obtained by 

 them from soils produced by disintegration of granite rocks. The 

 presence of potassium in plants is easily proved by burning them, 

 but the ashes, popularly called Potashes, will not contain the ele- 

 ment in the state in which it was in the plant during its life, but 

 in the state of a carbonate ; it is said to enable the plant to prepare 

 and form starch. The latter (sodium) enters largely into the composi- 

 tion of marine plants. 



Other elements in the composition of plants are iron, supposed to 

 be necessary to the formation of chlorophyll, copper, manganese, 

 and lithium, which last occurs in the ashes of the Grape Vine, 

 Tea, Coffee, and Tobacco plants, in the milk of cows which have 

 fed on plants growing in soils containing lithium, and in moor 

 water, and is one of the most widely distributed elements. 



Carbon, hydrogen, oxygen, and nitrogen have been called the 

 organic elements or organogens • sulphur and phosphorus have been 

 called pseudo-organic elements; and calcium, aluminium, magnesium, 

 potassium, sodium, iodine, bromine, silicon, iron, copper, manganese, 

 and lithium, have been called the inorganic elements. The distinc- 

 tion is not a desirable one, to say the least, since, whether any of 

 them are essential to plant life, and others only partially and not 

 universally present in plant structure, it seems apparent that, as soon 

 as any plant has utilised any one of the so-called inorganic elements, 

 it has then formed as much a part of the organic structure of the 

 plant as carbon, hydrogen, &c. The only way out of the difficulty 

 is to avoid the use of the words organic and pseudo-organic as in- 

 applicable to the above elements in reference to plant life. 



Some knowledge of the atmosphere by which our world is sur- 

 rounded will soon be found necessary. The atmosphere or air is 

 composed of the gases nitrogen, oxygen, aqueous vapour or vapour of 



