THE ELEMENTS OF PLANT FOOD. 83 



tissues and products ; and subsisting as we do upon plants, we 

 draw support indirectly from the insensible rocks. The plant 

 consumes the rock-dust, and attracts to itself the carbon of air 

 and earth ; we transform these into flesh and bones, and, as a 

 last step in this perpetual circulation of matter, after death they 

 relapse again into their dead inorganic condition. 



It was formerly thought by chemists that plants lived upon 

 humus, a compound entirely organic in its nature, and when 

 some of the metals were found in the ash of plants they were 

 regarded as accidental ingredients or extraneous bodies which 

 somehow intruded themselves into the incinerated mass. In our 

 time, we know that these mineral bodies enter the vegetable 

 structure as food, and that it cannot exist without them. The 

 mineral portion of plants is small indeed compared with the 

 nitrogenized and carbonaceous parts, and this paucity of the 

 mineral substances was undoubtedly the reason why the early 

 experimenters were led into error. 



At present we are acquainted with sixty-three elements or 

 primary bodies, of which all things, animate and inanimate, are 

 made. Twenty- two of these have been found in plants, and 

 therefore are to be regarded as food material. Let us for a 

 moment consider the strange metals and other substances which 

 plants absorb into their structures. Among the metals we find 

 iron, potassium, calcium, sodium, magnesium, manganese, cop- 

 per, caesium, rubidium and zinc. It has been stated that arsenic 

 has been found in plants, but this is doubtful. The non-met- 

 als are iodine, bromine, fluorine, chlorine, phosphorus, silicon, 

 carbon, hydrogen, nitrogen, oxygen and sulphur. Nothing can 

 appear more singular than the fact that the refractory metal, 

 iron, can find its way into the stalks and leaves of plants, or 

 that the rarer metals should be hunted out of the soil by them 

 and appropriated as food. Some varieties of plants have peculiar 

 appetites and require most extraordinary elements in order to 

 thrive. Tobacco is one of these, and the ash which clings to 

 the end of the smoker's cigar contains substances found in but 

 one or two other plants known to man. Among the rarer bod- 

 ies are the newly discovered metals caesium and rubidium, and 

 how or where the plant obtains them is indeed a mystery, as the 

 most delicate chemical tests have failed to detect these elements 

 in soils. In common garden beets, also, the same substances 



