1. FATTY ACID OCCURRENCE AND DISTRIBUTION
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the same degree of differentiation as have the depot fats. Nevertheless
the waxes of acid-fast bacteria, which consist of the high molecular
weight mycolic acids combined with polysaccharides, contrast sharply
with those of the rest of the plant and animal world. The waxes of
higher plants and insects appear to have similar fatty acids, namely
the C 24 to C 34 n-saturated acids with perhaps the corresponding
ω-hydroxy acids (23). In the phanerogams, the seed lipids of Simmondsia californica, which are waxes consisting mainly of eicos-11enoic acid combined with docosenol (263), form a remarkable variation from the other seed lipids, which are invariably glyceridic. The
depot lipids of the sperm whale likewise provide an exception in the
animal kingdom in consisting of waxes of unsaturated alcohols combined with Cio-Ci 8 n-saturated and Ci 4 -C 22 unsaturated acids, as in
the fats of marine fish.
The waxlike secretions of the skin (304, 305, 334), hair, and preen
glands (336-338) afford a unique variety of branched, n-odd-numbered
saturated and unsaturated fatty acids, the proportions and nature of
which appear to vary from one species to another. As many of these
acids are not found in the diet, the fatty acid composition could possibly be used to characterize the species.
The value of the fatty acids in waxes as a guide to the classification
of species still remains to be explored.
The limited data on seed phospholipids show that their fatty acid
composition is similar to that of the corresponding glycerides. In the
animal kingdom, the phospholipids of aquatic and terrestrial species
show no marked differences, the amounts of C 20 and C 22 highly
unsaturated acids in both being considerable. As these acids are absent from land plant lipids, the fatty acid composition of phospholipids
of land plants and animals shows a greater divergence than between
the corresponding glycerides.
The sphingolipids are not found in plants and these, together with
their characteristic fatty acids, including tetracosanoic, a-hydroxytetracosanoic, tetracos-15-enoic, and a-hydroxytetracos-15-enoic acids serve to
differentiate animals from plants.
E. CONCLUDING REMARKS
If evolution applies to morphology, it could be expected to apply
also to the chemical constitution of organisms. Gibbs (354) has recently summarized the attempts made by chemists and botanists to
relate the chemical characteristics of plants to their classification. The
results so far obtained have not provided a clear indication of biochemical evolution in plants, possibly because of the absence of ade-
91
the same degree of differentiation as have the depot fats. Nevertheless
the waxes of acid-fast bacteria, which consist of the high molecular
weight mycolic acids combined with polysaccharides, contrast sharply
with those of the rest of the plant and animal world. The waxes of
higher plants and insects appear to have similar fatty acids, namely
the C 24 to C 34 n-saturated acids with perhaps the corresponding
ω-hydroxy acids (23). In the phanerogams, the seed lipids of Simmondsia californica, which are waxes consisting mainly of eicos-11enoic acid combined with docosenol (263), form a remarkable variation from the other seed lipids, which are invariably glyceridic. The
depot lipids of the sperm whale likewise provide an exception in the
animal kingdom in consisting of waxes of unsaturated alcohols combined with Cio-Ci 8 n-saturated and Ci 4 -C 22 unsaturated acids, as in
the fats of marine fish.
The waxlike secretions of the skin (304, 305, 334), hair, and preen
glands (336-338) afford a unique variety of branched, n-odd-numbered
saturated and unsaturated fatty acids, the proportions and nature of
which appear to vary from one species to another. As many of these
acids are not found in the diet, the fatty acid composition could possibly be used to characterize the species.
The value of the fatty acids in waxes as a guide to the classification
of species still remains to be explored.
The limited data on seed phospholipids show that their fatty acid
composition is similar to that of the corresponding glycerides. In the
animal kingdom, the phospholipids of aquatic and terrestrial species
show no marked differences, the amounts of C 20 and C 22 highly
unsaturated acids in both being considerable. As these acids are absent from land plant lipids, the fatty acid composition of phospholipids
of land plants and animals shows a greater divergence than between
the corresponding glycerides.
The sphingolipids are not found in plants and these, together with
their characteristic fatty acids, including tetracosanoic, a-hydroxytetracosanoic, tetracos-15-enoic, and a-hydroxytetracos-15-enoic acids serve to
differentiate animals from plants.
E. CONCLUDING REMARKS
If evolution applies to morphology, it could be expected to apply
also to the chemical constitution of organisms. Gibbs (354) has recently summarized the attempts made by chemists and botanists to
relate the chemical characteristics of plants to their classification. The
results so far obtained have not provided a clear indication of biochemical evolution in plants, possibly because of the absence of ade-