Source, Etc

The flax plant, Linum usitatissimum, Linne (N.O. Linece), is a tall, erect annual, spread by cultivation over all temperate and tropical regions. Not only has the plant been known and cultivated for so many centuries that its geographical origin cannot be identified, but the use of its fibre can be traced back to the thirteenth or fourteenth century before the Christian era. Flax seeds, as well as cloth woven from flax, have been found in Egyptian tombs, and the process of weaving is depicted on their buildings. The seeds were used as a food; the medicinal use of the mucilage and the value of the oil contained in them appear not to have been known till later. The flax plant bears a small globular capsular fruit containing ten seeds; these are separated when ripe. Argentina, Russia, Canada, India, the United States and Holland furnish the principal supplies.

Description

The seeds are commonly dark brown in colour, smooth and shining. They are elongated ovoid, flattened, with an acute edge; from 4 to 6 mm. long. One end is rounded, but the other has an oblique point, on one side of which, just below the apex, is a slight depression. In this depression both hilum and micropyle are situated, the seed being anatropous. The surface of the seed is glossy and minutely pitted. A transverse section exhibits a yellowish white oily kernel consisting of two large cotyledons surrounded by a narrow endosperm (not always easily seen). Soaked in water the seeds lose their glossy appearance and become covered with mucilage. They have but a slight odour, and an oily, mucilaginous taste.

Both in colour and size linseed exhibits notable variations according to its source. As a general rule, warm climates yield larger and paler seeds than cold climates.

The student should observe

(a) The glossy 'pitted surface,

(b) The mucilage extracted by water,

(c) In the transverse section the two oily cotyledons and narrow endosperm (under a powerful lens).

Constituents

Linseed contains from 30 to 40 per cent, of fixed oil, about three-fourths of which can be extracted by pressure. The epidermis of the seed-coat contains mucilage (6 per cent.), which, together with the proteids (25 per cent.) present in the seed and part of the oil, are left in the cake obtained when the seeds are pressed. The presence of oil, proteid, and carbohydrate (mucilage) in the cake renders it valuable as a cattle food. Unripe seeds contain numerous small starch grains, but the ripe seeds are free from starch. The seeds also contain a cyanogenetic glucoside, linamarin, identical with phaseolunatin (compare p. 38).

The fixed oil (Oleum Lini, B.P.) consists chiefly of linolein, a mixture of the glyceryl esters of linolic, linolenic, and isolinolenic acids, the acids themselves being sometimes designated as linoleic acid; it also contains similar esters of oleic, stearic, palmitic, and myristic acids. On exposure to the air it slowly hardens to a varnish, a change due to the oxidation of the linolein. The oil is characterised by its high specific gravity (0.930 to 0.940) and high iodine value (not under 170). See also ' Linseed Oil.'

Fig. 86.   Linseed. Transverse section, showing the seed coats, endosperm, and cotyledons. Magnified. (Moeller).

Fig. 86. - Linseed. Transverse section, showing the seed-coats, endosperm, and cotyledons. Magnified. (Moeller).

The mucilage consists of a mixture of hexanes and pentanes corresponding to the formula 2(C6H10O5),2(C5H8O4); it yields by hydrolysis the sugars galactose, dextrose, arabinose, and xylose.

Crushed linseed, Lini Semina Contusa, B.P., consists of the seeds reduced to a coarse powder without being deprived of any part of their constituents. It should, when mixed with water, have a bland, not pungent (cruciferous seeds) or rancid (stale linseed) odour. It should yield not less than 30 per cent, of oil to carbon disulphide (indicating the absence of ground cake left after removal of part of the oil), and the oil thus extracted should respond to the official tests for Oleum Lini. It should not give the characteristic reactions with the tests for starch, nor leave, when incinerated, more than 5 per cent, of ash (absence of added starch and undue proportion of mineral matter). The presence of starch may be conveniently detected by microscopical examination or by applying the usual iodine test to a cooled decoction of the crushed Unseed previously freed from oil by treatment with ether or carbon disulphide.

Uses

Crushed linseed is used externally, in the form of a poultice, to convey heat and moisture to certain parts; the entire seeds are used to make a demulcent infusion containing a large quantity of mucilage.

Note

Linseed usually contains foreign (weed) seeds, the proportion of which should not exceed 4 per cent.; these weed seeds often afford a guide to the geographical source of the linseed.