190 THE CANADIAN NATURALIST. [June, 



plants are nourislied ; nor is it solely in quest of food, such as th« 

 leaves also can assimilate from the air, that the roots spread forth 

 their manifold ramifications amidst the earth. 



Liebeg first set forth, in all their peculiar interest and import- 

 ance, the fixed ingredients of plants ; that is the compounds which 

 appear as ash, when the volatilizable air-derived elements of plants 

 are burned off. These ash-ingredients constitute, as heexplained^ 

 the special (though not the sole) food of the roots; and they are 

 the only kind of nutriment which has its primary and excl >sivc 

 source in the soil. 



These essential ash-ingredients, so far as we yet know them, are 

 the two fixed alkalies, potash and soda ; two earthy bases, lime and 

 magnesia; one heavy metallic base, oxide of iron; three acids, 

 phosphoric, silicic, and sulphuric ; and lastly, chlorine, which, 

 though a gas, is always taken up by plants in fixed combinations 

 (as fo*" example in common salt), so as to remain in the ash or 

 incineration. 



Small as are the proportions of these fixed ingredients assimilated 

 by plants during their growth, they are yet as necessary to the 

 plant's development as the carbon and water which make up itg 

 main bulk. So again, as between the fixed ingredients themselves, 

 although some of them are needed in larger, and some in smaller 

 proportions, each species of plant having in this respect, its special 

 requirements; although, for example, one ingredient may form 

 more than one half the total ash of a given plant, and another 

 less than a tenth part thereof; yet are they all equally essential 

 to its development, which languishes as much for want of the mi- 

 nutest as of the bulkiest cinereal supply. Soils wholly deficient 

 in anyone of the ash ingredients of a particular plant, cannot pro- 

 duce that plant, howsoever abundantly every other of its elements, 

 volatile and fixed, may be supplied. Partial deficiency of either 

 of the normal ingredients of plant-food, whether fixed or volatile^ 

 involves a proportionately scanty crop; and no heaping of other 



carbonic acid, nitrogen, ammonia, and nitric acid, oxygen, hydrogen, 

 and water, all appertain to the mineral kingdom, in every sense as 

 fully as silica, potash, the phosphates, &c. The epithet "mineral" 

 applies therefore equally to all the elements, both volatile and fixed, of 

 plant-food; it is for the separate designation of the fixed or ash constitu- 

 ents, that the epithet cinereal is proposed. In this sense (to test iU 

 cpavenience) it will be employed in the remainder of thii section. 



