HIGHER AND LOWER PLANTS 
261 
construct proteids and carbohydrates as we are told our now 
automatic cousins were once taught to do; though man fails 
to consider that it may be a lost art, and the secret has died 
with the plants in a “ catagenetic ” decline. 
All plants and their products are composed of two general 
classes of compounds, — volatile and fixed. The former, on 
incineration of the plant, are transformed into gases, leaving 
the last as so-called ash-constituents. 
I will very briefly refer to the sources of the substances 
which go to the building of the plant structure. Green plants 
derive their carbon from the carbon dioxide of the atmosphere, 
and even from complex organic compounds, since Darwin 1 
has shown that insectivorous plants, by means of their modified 
leaves, are able to absorb flies and other small insects. 
Plants that do not contain chlorophyll, as fungi, take 
their carbon from complex compounds of * decaying organic 
matter. Not only do all the so-called organic compounds of 
plants contain carbon, but it is found also in the form of car¬ 
bonates . 2 
Hydrogen is absorbed by all plants in the form of water, 
or ammonia and its compounds, or in complex substances, 
as mentioned above. Oxygen is taken up by plants free or in 
combination, in water or in salts, and there are six possible 
sources of nitrogen supply; but I will not delay by going into 
this subject . 3 
Sulphur and phosphorus are constituents of proteids, and 
are derived from inorganic compounds. In addition to these 
the elements essential to the nutrition and maintenance of 
the life of all plants are potassium, calcium, magnesium, iron 
in the case of green plants, its absence producing the con¬ 
dition of etiolation; and, in certain cases, chlorine. Silicon, 
fluorine, manganese, sodium, lithium, rubidium, caesium, 
barium, strontium, aluminium, zinc, copper, arsenic, titanium, 
iodine, and bromine have also been found among the ash- 
ingredients of certain plants. 
1 Insectivorous Plants. 2 Ann. Phys. et Chim ., Berthelot. 
3 “ The Economical Aspect of Agr. Chem.,” by H. W. Wiley, Proc. A. A. 
A. S., vol. xxxv, 1886. 
