58 
POPULAR SCIENCE REYIEW. 
compounds. Let us now briefly examine part o# this series of 
changes, looking at the mineral food of plants and the elements 
which this food furnishes. We purpose to answer these two 
questions — What elements occur in plants?” and “ In what 
compounds must these elements be supplied?” 
It is usual to speak of the several constituents of which plants 
consist as organic and inorganic ; but the distinction is almost 
wholly false. All the constituents, or, we will rather say, all the 
elements found constantly in any species of plant are equally 
necessary to its organism ; to be such an organised structure as it 
is it must have, or have had, all of them, though in different propor- 
tions. The error has arisen partly from the fact that organic com- 
pounds (such as starch, cellulose, fibrin, &c.) found in plants, when 
quite pure leave no ash or incombustible mineral residue when 
burned; they contain only the four so-called organic elements, car- 
bon, hydrogen, oxygen, and nitrogen, and occasionally sulphur as 
well. But the so-called inorganic elements, the calcium, the potas- 
sium, the iron, &c., are as essential to the organism of the plant as 
the carbon and hydrogen. The living plant cannot exist without 
them — cannot perform its functions in their absence, although 
the dead organic products derived from the plants maybe obtained 
free from all these incombustible or ash constituents. By the 
earlier plant analysts the presence of these cinereal matters, often 
so minute in quantity, was considered accidental ; it was thought 
that they were absorbed by chance along with the true organic nu- 
triment of the plant. This organic nutriment theory has itself also 
been at last abandoned, and very few chemists retain any remnant 
of the old view that plants live upon humus,” itself one of the 
first products of the decay of vegetable matter. 
A good division of the elements of a plant, if we must have a 
division, is into (1) the volatile, dr combustible; (2) the non- 
volatile, or incombustible. Of course, some of the constituent 
elements, like oxygen and sulphur, will partly escape, among the 
volatile products when a plant is burnt, and partly remain in the 
ash ; still there is some convenience in this classification, and it 
is often adopted. Below is a list of all the elements found in 
plants, and their symbols, arranged into a volatile and a non- 
volatile group : — 
Volatile Elements. 
Carbon, 0. 
Hydrogen, II. 
Nitrogen, N. 
Oxygen, 0. 
Sulphur, S. 
Non-Volatile Elements. 
Silicon, Si. 
Phosphorus, P. 
Chlorine, Cl. 
Potassium, K. 
Calcium, Ca. 
Sodium, Na. 
Iron, Fe. 
Magnesium, Mg. 
Manganese, Mn. 
Fluorine, F. 
^Bromine, Br. 
*Iodine, I. 
^Aluminium, Al. 
*Zinc, Zn. 
* Caesium, Cs. 
^Rubidium, Rb. 
^Copper, Cii. 
