1. FATTY ACID OCCURRENCE AND DISTRIBUTION
3
in some species, notably in the Euphorbiaceae, the conjugated Ci 8
trienoic-a-eleostearic (octadeca-cis-9,irans-11,frans-13-trienoic) acid, is
prominent. As examples of the diversity of the plant fatty acids, the
occurrence may be mentioned, in a limited number of species, of
hydroxy-substituted and keto-substituted unsaturated acids, unsaturated
acids with acetylenic linkages, and acids with cyclopentene and cyclopropane rings, as well as epoxy unsaturated acids described in the next
section.
In aquatic life there is no marked distinction between the fats of
plants and animals. Throughout the whole of aquatic life the pattern of
fatty acid composition is uniform, apart from minor differences between marine and freshwater species. The distinctive nature of the fat
of aquatic species, which includes low amounts (15^20%) of saturated
acids, mainly palmitic acid, together with a wide range (C14-C22) of
unsaturated acids, makes it desirable to discuss the fats of aquatic
species separately from those of terrestrial plants and animals.
Our knowledge of the composition of naturally occurring fats is
based on the study of relatively few species and has been confined
more or less to seed fats and animal depot fats, including fish oils,
which are of actual or potential industrial importance. Much information has been obtained on the tissues and organs of rats because of the
widespread use of this animal for experimental purposes, but little is
known about the fatty substances of the lower forms of plant life. In
the higher plants, the lipids in parts other than the seeds, including
leaves, roots, and flowers, have received scant attention. The organ fats
of animals as compared with their depot fats have been neglected.
The most recent comprehensive account of the distribution and occurrence of fatty acids is in Hilditch's (3) "Chemical Constitution of
Natural Fats." Hilditch makes it evident that there is a broad pattern
of fatty acid types and distribution, which fits into the phylogenetic
scale and also follows a classification of species based on morphological
grounds. This pattern shows the tendency of the more complex and
highly developed forms of life to elaborate the simplest types of fat.
However, in the animal world, as will be discussed later, fats are derived directly from the dietary fats as well as endogenously produced,
so that the fats found in the body depend to some extent on those
present in the diet.
Studies on the classification of species and the composition of the
fats that they elaborate have been based to a large extent on the examination of fats from an individual specimen or from bulk samples
comprising many individuals. Little attention has been paid to the
possibility of variation between individuals within a given species. It
3
in some species, notably in the Euphorbiaceae, the conjugated Ci 8
trienoic-a-eleostearic (octadeca-cis-9,irans-11,frans-13-trienoic) acid, is
prominent. As examples of the diversity of the plant fatty acids, the
occurrence may be mentioned, in a limited number of species, of
hydroxy-substituted and keto-substituted unsaturated acids, unsaturated
acids with acetylenic linkages, and acids with cyclopentene and cyclopropane rings, as well as epoxy unsaturated acids described in the next
section.
In aquatic life there is no marked distinction between the fats of
plants and animals. Throughout the whole of aquatic life the pattern of
fatty acid composition is uniform, apart from minor differences between marine and freshwater species. The distinctive nature of the fat
of aquatic species, which includes low amounts (15^20%) of saturated
acids, mainly palmitic acid, together with a wide range (C14-C22) of
unsaturated acids, makes it desirable to discuss the fats of aquatic
species separately from those of terrestrial plants and animals.
Our knowledge of the composition of naturally occurring fats is
based on the study of relatively few species and has been confined
more or less to seed fats and animal depot fats, including fish oils,
which are of actual or potential industrial importance. Much information has been obtained on the tissues and organs of rats because of the
widespread use of this animal for experimental purposes, but little is
known about the fatty substances of the lower forms of plant life. In
the higher plants, the lipids in parts other than the seeds, including
leaves, roots, and flowers, have received scant attention. The organ fats
of animals as compared with their depot fats have been neglected.
The most recent comprehensive account of the distribution and occurrence of fatty acids is in Hilditch's (3) "Chemical Constitution of
Natural Fats." Hilditch makes it evident that there is a broad pattern
of fatty acid types and distribution, which fits into the phylogenetic
scale and also follows a classification of species based on morphological
grounds. This pattern shows the tendency of the more complex and
highly developed forms of life to elaborate the simplest types of fat.
However, in the animal world, as will be discussed later, fats are derived directly from the dietary fats as well as endogenously produced,
so that the fats found in the body depend to some extent on those
present in the diet.
Studies on the classification of species and the composition of the
fats that they elaborate have been based to a large extent on the examination of fats from an individual specimen or from bulk samples
comprising many individuals. Little attention has been paid to the
possibility of variation between individuals within a given species. It