1. FATTY ACID OCCURRENCE AND DISTRIBUTION
43
lationships. Bark, stem, root, and flower fats have not been found to
contain any but the common acids, apart from erucic acid which has
been found in the roots of the mangel (Beta rapa milgaris) (220).
It is not feasible here to provide details of the extensive data on
phanerogam fats, for which the reader is referred to the comprehensive
and complete treatise by Hilditch (3). The data regarding the seed
fats in particular are now voluminous, and in this section it has been
necessary to select examples, rather than cover the whole field. In the
grouping of seed fats according to the main fatty acid components, the
writer has followed essentially the classification described by Hilditch
(θ).
a. Leaf Fats. The leaf fats of only a few species, including especially
pasture plants, have been studied. It appears that the lipid content does
not usually exceed 7% and that rather less than half of the total lipids
are triglycerides (221). The remainder comprises waxes, phospholipids,
and unsaponifiable matter. The analysis of the glycerides of ryegrass
(Lolium perenne) shown in Table VIII may be used to illustrate the
fatty acid composition of leaf fats.
The above analysis is supported by that of Hilditch and Jasperson
(222) for grass fatty acids, using similar alkali-isomerization techniques
in association with ester fractionation. Earlier work on the leaf glycerides of orchardgrass (cocksfoot) (Dactylis glomerata) (223, 224)
and ryegrass (223), as well as on mixed pasture species (225), also
shows a similar fatty acid composition; but the rather lower proportions
of linolenic acid reported are perhaps to be ascribed to the use of the
Kaufmann thiocyanogen method in place of the more recent spectroscopic techniques.
The fatty acid composition of the leaf fats of the Cruciferae appears
to be similar to that of the Gramineae as shown by the results obtained
by Chibnall and Channon (226) for cabbage (Brassica oleracea) leaf
and for rape (Brassica napus) leaf by Shorland (32, 227). However,
in the rape leaf, in addition to a high content of highly unsaturated Ci 8
acids, there were also substantial amounts (11-17%) of Ci 6 unsaturated
acids consisting mainly of hexadeca-7,10,13-trienoic acid which could
not be found in ryegrass and appears to be characteristic of rape leaf.
Other leaf fats examined, including those of spinach (Spinacea oleracea)
(228), lucerne (Medicago sativa) (229), and buckwheat (Polygonum
fagopyrum) (230), also show that linolenic acid is the main constituent,
though in these species oleic acid is a more important constituent than
in the grasses. It is perhaps relevant that oleic acid itself has not been
isolated from grass lipids, and the only evidence, apart from physical
measurements, on the mixed acids is the isolation of traces of the
43
lationships. Bark, stem, root, and flower fats have not been found to
contain any but the common acids, apart from erucic acid which has
been found in the roots of the mangel (Beta rapa milgaris) (220).
It is not feasible here to provide details of the extensive data on
phanerogam fats, for which the reader is referred to the comprehensive
and complete treatise by Hilditch (3). The data regarding the seed
fats in particular are now voluminous, and in this section it has been
necessary to select examples, rather than cover the whole field. In the
grouping of seed fats according to the main fatty acid components, the
writer has followed essentially the classification described by Hilditch
(θ).
a. Leaf Fats. The leaf fats of only a few species, including especially
pasture plants, have been studied. It appears that the lipid content does
not usually exceed 7% and that rather less than half of the total lipids
are triglycerides (221). The remainder comprises waxes, phospholipids,
and unsaponifiable matter. The analysis of the glycerides of ryegrass
(Lolium perenne) shown in Table VIII may be used to illustrate the
fatty acid composition of leaf fats.
The above analysis is supported by that of Hilditch and Jasperson
(222) for grass fatty acids, using similar alkali-isomerization techniques
in association with ester fractionation. Earlier work on the leaf glycerides of orchardgrass (cocksfoot) (Dactylis glomerata) (223, 224)
and ryegrass (223), as well as on mixed pasture species (225), also
shows a similar fatty acid composition; but the rather lower proportions
of linolenic acid reported are perhaps to be ascribed to the use of the
Kaufmann thiocyanogen method in place of the more recent spectroscopic techniques.
The fatty acid composition of the leaf fats of the Cruciferae appears
to be similar to that of the Gramineae as shown by the results obtained
by Chibnall and Channon (226) for cabbage (Brassica oleracea) leaf
and for rape (Brassica napus) leaf by Shorland (32, 227). However,
in the rape leaf, in addition to a high content of highly unsaturated Ci 8
acids, there were also substantial amounts (11-17%) of Ci 6 unsaturated
acids consisting mainly of hexadeca-7,10,13-trienoic acid which could
not be found in ryegrass and appears to be characteristic of rape leaf.
Other leaf fats examined, including those of spinach (Spinacea oleracea)
(228), lucerne (Medicago sativa) (229), and buckwheat (Polygonum
fagopyrum) (230), also show that linolenic acid is the main constituent,
though in these species oleic acid is a more important constituent than
in the grasses. It is perhaps relevant that oleic acid itself has not been
isolated from grass lipids, and the only evidence, apart from physical
measurements, on the mixed acids is the isolation of traces of the