2 3 4 PLANT AND ORGANIC CHEMISTRY 
Most of the ash-constituents essential or injurious to the 
growth and development of plants are known, and also the va¬ 
riations in growth caused by the presence or absence of certain 
inorganic compounds. 
The chemical changes through which many plants pass from 
the germination of their seed to maturity and decay are also 
known, each separate stage of growth showing a distinct chem¬ 
ical composition or a predominance of some one chemical com¬ 
pound. 
It should be especially noted that some chemical compounds 
occur in certain species of plants and do not occur in others. 
Certain classes of compounds are found widely distributed 
through the plant kingdom, accompanied by correlated mor¬ 
phological characters. Some one compound, as saponin, will 
be found with similar botanical characters in plants of distinct 
genera and families, on the same plane of evolution or devel¬ 
opment. 
It cannot be the result of accident that cinchona and related 
plants contain quinine; and other plants, distributed through 
the vegetable kingdom, their own typical compounds. Nor can 
it be the result of accident, or changes produced by climate 
or other causes, that an absence of some one or more com¬ 
pounds is accompanied by a modification of the exterior of 
the plant. 
Before taking up the consideration of the above statements 
in detail, it may be well to study briefly two properties 1 of liv¬ 
ing protoplasm, namely, absorption and metabolism. 
The seeds of plants are the storehouses of a certain amount 
of latent energy or life, elaborated by the parent plant and 
stored up in the form of complex chemical compounds. Under 
suitable conditions of warmth and moisture, certain chemical 
changes take place within the seed. The latent energy becomes 
active, and the seedling grows, feeding upon its food supply 
until it has exhausted its store. 
At this stage the little plant must seek its food from without, 
from the atmosphere and the soil. The soil is of varying and 
complex composition, containing, between its particles, gases 
1 Lectures on the Physiology of Plants, by S. H. Vines. Cambridge, 1886. 
