1. FATTY ACID OCCURRENCE AND DISTRIBUTION
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In the trienoic series linolenic (octadeca-9,12,15-trienoic) acid is
found in many seed fats as well as in the lipids of some cryptogams.
The related hexadeca-7,10,13-trienoic acid has been found in rape leaf,
but not in the seed fats (32, 227). Other nonconjugated trienoic acids
include octadeca-6,9,12-trienoic acid found in the seed fats of Oenothera biennis (234, 235).
In the seed fats of the Rosaceae, Euphorbiaceae, and Cucurbitaceae
some of the species contain as major constituents a-eleostearic (octadecacis-9,tran$-ll,trans-13-trienoic)
acid or similar conjugated acids including 18-hydroxy-a-eleostearic and parinaric (octadeca-9,11,13,15-tetraenoic) acid, replacing entirely or partly linolenic acid (37). As a further variation there occurs in Calendula officinalis (Compositae) octadec3.-trans-8,trans-10,trans-12-trienoic acid (250). The occurrence of trienoic acids with conjugated double bonds in the seed fats of species of
the families mentioned above provides a unique differentiation from
the rest of the animal and plant world. However, the absence of such
acids in some of the species somewhat reduces their value as a complete
guide to their botanical classification.
The sporadic and rare occurrence of acids containing acetylenic bonds,
such as tariric (octadec-6-ynoic) acid in the genus Picramnia (Simarubaceae) (257), 8-hydroxyoctadec-17-en-9,ll-diynoic acid in Onguekoa
gore (Olacaceae) seed oil (258) and octadec-ll-en-9-ynoic acid (43,
44) in Ximenia (Olacaceae) as well as in Santalaceae species (260,
261) affords an interesting diversion, the value of which in botanical
classification is not clear.
Several unusual hydroxy-substituted unsaturated acids of limited
occurrence have been mentioned above. To these may be added
ricinoleic (12-hydroxyoctadec-9-enoic) acid present as the main constituent of castor (Ricinus communis) (Euphorbiaceae) seed oil (3), and
its isomer 9-hydroxyoctadec-12-enoic acid present in the seed oils of
Strophanus sarmentosus (25) (Apocynaceae). The related oxygenated
acid vernolic (12,13-epoxyoctadec-9-enoic) acid occurs in Vernonia
anihelmintica (26) (Compositae), Cephalocroton cordofanus (Euphorbiaceae) (245), and in Hibiscus esculentus Linn. (Malvaceae) (253).
The appearance of unusual hydroxy or epoxy acids in apparently isolated species in several different families would appear to show an absence of correlation between the occurrence of chemical constituents
and biological classification.
3. Branched-Chain Acids
The occurrence of branched-chain fatty acids in more than minor
amounts is restricted. Isovaleric acid is found in quantity in the depot
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In the trienoic series linolenic (octadeca-9,12,15-trienoic) acid is
found in many seed fats as well as in the lipids of some cryptogams.
The related hexadeca-7,10,13-trienoic acid has been found in rape leaf,
but not in the seed fats (32, 227). Other nonconjugated trienoic acids
include octadeca-6,9,12-trienoic acid found in the seed fats of Oenothera biennis (234, 235).
In the seed fats of the Rosaceae, Euphorbiaceae, and Cucurbitaceae
some of the species contain as major constituents a-eleostearic (octadecacis-9,tran$-ll,trans-13-trienoic)
acid or similar conjugated acids including 18-hydroxy-a-eleostearic and parinaric (octadeca-9,11,13,15-tetraenoic) acid, replacing entirely or partly linolenic acid (37). As a further variation there occurs in Calendula officinalis (Compositae) octadec3.-trans-8,trans-10,trans-12-trienoic acid (250). The occurrence of trienoic acids with conjugated double bonds in the seed fats of species of
the families mentioned above provides a unique differentiation from
the rest of the animal and plant world. However, the absence of such
acids in some of the species somewhat reduces their value as a complete
guide to their botanical classification.
The sporadic and rare occurrence of acids containing acetylenic bonds,
such as tariric (octadec-6-ynoic) acid in the genus Picramnia (Simarubaceae) (257), 8-hydroxyoctadec-17-en-9,ll-diynoic acid in Onguekoa
gore (Olacaceae) seed oil (258) and octadec-ll-en-9-ynoic acid (43,
44) in Ximenia (Olacaceae) as well as in Santalaceae species (260,
261) affords an interesting diversion, the value of which in botanical
classification is not clear.
Several unusual hydroxy-substituted unsaturated acids of limited
occurrence have been mentioned above. To these may be added
ricinoleic (12-hydroxyoctadec-9-enoic) acid present as the main constituent of castor (Ricinus communis) (Euphorbiaceae) seed oil (3), and
its isomer 9-hydroxyoctadec-12-enoic acid present in the seed oils of
Strophanus sarmentosus (25) (Apocynaceae). The related oxygenated
acid vernolic (12,13-epoxyoctadec-9-enoic) acid occurs in Vernonia
anihelmintica (26) (Compositae), Cephalocroton cordofanus (Euphorbiaceae) (245), and in Hibiscus esculentus Linn. (Malvaceae) (253).
The appearance of unusual hydroxy or epoxy acids in apparently isolated species in several different families would appear to show an absence of correlation between the occurrence of chemical constituents
and biological classification.
3. Branched-Chain Acids
The occurrence of branched-chain fatty acids in more than minor
amounts is restricted. Isovaleric acid is found in quantity in the depot