1. FATTY ACID OCCURRENCE AND DISTRIBUTION
51
composition of phanerogam fats. In view of the extensive and varied
nature of the data discussed in the present section it is perhaps advisable to summarize the main conclusions that emerge.
In the seed fats of many species, as in the leaf and fruit-coat fats,
the fatty acids are often limited to the unsaturated acids, oleic and
linoleic (sometimes with linolenic acid), and palmitic acid is the chief
saturated acid. However, in other species there are found in the seed
fats specific fatty acids characteristic of the family or the genus. Thus
the occurrence of petroselinic acid is characteristic of the Umbelliferae,
chaulmoogric and similar cyclopentenyl fatty acids are found only in
the Flacourtiaceae. In the Cruciferae, Hilditch (3) lists the seed fats
of five species of Brassica and eleven other genera of the family. In
all but one species, Hesperis matronalis, erucic acid occurs and is
usually a major constituent. A high content of myristic acid likewise is
found in the seed fats of all species of Myristicaceae, and seed fats of
various Palmae show a great similarity in fatty acid composition as
well as a high (approximately 45%) lauric acid content. These examples show a striking correlation between the chemical and morphological classification of species. There are, however, other examples
where the correlation is more limited or even absent. In the Euphorbiaceae, Hilditch (3) lists the fatty acid composition of 33 species belonging to 21 genera. The polyunsaturated acids, which are typically the
main constituents, comprise in some species linolenic acid, in others
α-eleostearic acid, or as in Mallotus philippinensis, ω-hydroxyeleostearic
acid. Again, polyunsaturated acids may be absent and their place be
taken by unusual acids such as ricinoleic in castor (Ricinus communis)
oil, or epoxyoleic acid in Cephalocroton cordofanus. However, if the
fatty acid composition of individual genera is considered, there is considerable specificity. In the genus Aleurites, for example, four different
species are listed. In three, the major fatty acid is α-eleostearic. In the
other species α-eleostearic acid is absent, being replaced by linolenic
acid. In the genus Euphorbia the four species listed all contain linolenic
acid as the only polyunsaturated constituent. The Simarubaceae include
a diversity of seed fats in the different species. Those of the genus
Picramnia contain tariric acid; those of Irvingia, myristic and lauric;
those of Ficrasma, petroselinic acid; and other genera have seed fats
that are classifiable into the large category of the palmitic-oleic-linoleic
group.
The discovery of a new or unusual fatty acid in a seed fat does not
necessarily place the plant in a particular botanical family or signify
the genus or species to which it belongs. Vernolic acid, which was
earlier considered to be specific for the seed fat of Vernonia anthel-
51
composition of phanerogam fats. In view of the extensive and varied
nature of the data discussed in the present section it is perhaps advisable to summarize the main conclusions that emerge.
In the seed fats of many species, as in the leaf and fruit-coat fats,
the fatty acids are often limited to the unsaturated acids, oleic and
linoleic (sometimes with linolenic acid), and palmitic acid is the chief
saturated acid. However, in other species there are found in the seed
fats specific fatty acids characteristic of the family or the genus. Thus
the occurrence of petroselinic acid is characteristic of the Umbelliferae,
chaulmoogric and similar cyclopentenyl fatty acids are found only in
the Flacourtiaceae. In the Cruciferae, Hilditch (3) lists the seed fats
of five species of Brassica and eleven other genera of the family. In
all but one species, Hesperis matronalis, erucic acid occurs and is
usually a major constituent. A high content of myristic acid likewise is
found in the seed fats of all species of Myristicaceae, and seed fats of
various Palmae show a great similarity in fatty acid composition as
well as a high (approximately 45%) lauric acid content. These examples show a striking correlation between the chemical and morphological classification of species. There are, however, other examples
where the correlation is more limited or even absent. In the Euphorbiaceae, Hilditch (3) lists the fatty acid composition of 33 species belonging to 21 genera. The polyunsaturated acids, which are typically the
main constituents, comprise in some species linolenic acid, in others
α-eleostearic acid, or as in Mallotus philippinensis, ω-hydroxyeleostearic
acid. Again, polyunsaturated acids may be absent and their place be
taken by unusual acids such as ricinoleic in castor (Ricinus communis)
oil, or epoxyoleic acid in Cephalocroton cordofanus. However, if the
fatty acid composition of individual genera is considered, there is considerable specificity. In the genus Aleurites, for example, four different
species are listed. In three, the major fatty acid is α-eleostearic. In the
other species α-eleostearic acid is absent, being replaced by linolenic
acid. In the genus Euphorbia the four species listed all contain linolenic
acid as the only polyunsaturated constituent. The Simarubaceae include
a diversity of seed fats in the different species. Those of the genus
Picramnia contain tariric acid; those of Irvingia, myristic and lauric;
those of Ficrasma, petroselinic acid; and other genera have seed fats
that are classifiable into the large category of the palmitic-oleic-linoleic
group.
The discovery of a new or unusual fatty acid in a seed fat does not
necessarily place the plant in a particular botanical family or signify
the genus or species to which it belongs. Vernolic acid, which was
earlier considered to be specific for the seed fat of Vernonia anthel-