climatic conditions, as indicated by the fact
that most spice plants are tropical in habit, rather than the result of
their protective influence in the struggle for survival during past ages.

Many of the oils and resins which are secreted as the result of injury by
disease or wounds have marked antiseptic properties and undoubtedly serve
to prevent the entrance into the injured tissue of destructive organisms.

But apart from these possible protective influences which may have had an
important effect upon the preservation and perpetuation of the species of
plants which secrete them, there is no known biological necessity for the
presence of these aromatic substances in plants.

REFERENCES

ABDERHALDEN, E.--"Biochemisches Handlexikon, Band 7, Gerbstoffe,
Flechtenstoffe, Saponine, Bitterstoffe, Terpene, Aetherische Oele, Harze,
Kautschuk," 822 pages, Berlin, 1912.

ALLEN'S Commercial Organic Analysis, Vol. IV, "Resins, Rubber, Guttapercha,
and Essential Oils," 461 pages, 7 figs., Philadelphia, 1911 (4th ed.).

HEUSLER, F., trans. by Pond, F. J.--"The Chemistry of the Terpenes," 457
pages, Philadelphia, 1902.

PARRY, E. J.--"The Chemistry of Essential Oils and Perfumes," 401 pages, 20
figs., London, 1899.

CHAPTER XII

THE VEGETABLE BASES

We come, now, to the consideration of the characteristically nitrogenous
compounds of plants. None of the groups of compounds which have been
considered thus far have, as a group, contained the element nitrogen. This
element is present in the chlorophylls and in certain other pigments, but
not as the characteristic constituent of the molecular structure of the
group of compounds, nor do these compounds serve as the source of supply of
nitrogen for the plant's needs.

The characteristic nitrogen-containing compounds may all be regarded as
derived from ammonia, or ammonium hydroxide, by the replacement of one or
more hydrogen atoms with organic radicals of varying type and complexity.
If the group, or groups, which be considered as having replaced a hydrogen
atom in ammonia, in such compounds, is an alkyl group, the compound is
strongly basic in character and is known as an _amine_; whereas if the
replacing group is an acid radical, the resulting compound may be neutral
(known as _acid amides_), or weakly acid (known as _amino-acids_) in type.
Compounds of the first type const