The Fruit of Opuntia Vulgaris, Lin.
BY WILLIAM W. LIGHT, PH.G.
From an Inaugural Essay.
The fruit begins to appear in July and ripens about the middle of October. It is about an inch in length, one-half to three-fourths of an inch in thickness, roundish pear-shaped, marked at the apex with concentric rings, and beset with rudimentary bristles in spiral rows. It is crimson externally, and internally of a still brighter color and frosty, sparkling appearance, it is covered with a thin tough skin, underlying which is a thickish pulpy rind. The berry-like fruit is filled with seeds arranged in longitudinal rows imbedded in and surrounded by a fleshy mucilaginous pulp and separated by white dissepiments. The seeds are from eight to twenty in number, in five rows alternately arranged with one capping-seed, to which the tough epidermis, in the centre of the umbilicated apex of the fruit, is attached. The seeds are flattish, circular and uneven, one-eighth to three-sixteenths of an inch in diameter and fully one-eighth of an inch through the thickest part. The seed is anatropous. The rhaphe forms a prominent bony margin nearly around the entire seed. The testa is cartilaginous, of uneven thickness and of a whitish color. The portion immediately surrounding the chalaza is very thin and is translucent. The membraneous tegmen of the seed is of a shining blackish brown color, which is plainly visible through the thin portion of the testa and gives that part of the seed a bluish black appearance. The embryo is imbedded in the oily albumen and has the cotyledons set contrary to the sides of the seed. It forms a little more than a complete circle and encloses a white, starchy centre. The fruit has an agreeable, slightly acid and very mucilaginous taste and a refreshing odor. It is frequently eaten, the seeds of necessity swallowed whole as it would be almost impossible to crush their shell-like testa between the teeth, or to separate them from their mucilaginous envelope.
The ripe fruit contains 68.2 per cent. of moisture. The ash amounted to 1.76.per cent. of the entire fresh fruit. It consists largely of silica, besides carbonates, chlorides, sulphates and phosphates, with potassium, sodium, aluminium, iron, magnesium and calcium. The seeds are about one-sixth the weight of the entire fruit.
The seeds and enveloping pulp were placed in a coarse linen bag to remove the mucilaginous matter by maceration in water. The mucilage had an acid reaction and possessed a beautiful light crimson color which was completely discharged by heating on a water-bath or by the addition of an alkali.
The mucilage was not affected by oxalate of ammonium or concentrated solutions of ferric chloride or of sodium borate, but a precipitate was formed with both the normal and the basic lead acetate. The mucilage was precipitated by alcohol, obtained on a filter, dried in scales over a water-bath and preserved for further examination. The filtrate from the mucilage responded clearly to tests for glucose and pectous compounds but contained no tannin. The skins with a portion of the pulp left after the removal of the seed, were macerated in alcohol for several days the filtered product being a wine-red tincture of a pleasant fruit-like odor and acid reaction to litmus. This tincture was diluted with water and the alcohol distilled off on a water-bath. In this operation the wine-red color was discharged, the liquid assuming a green and then a light straw color. After removing the coloring-matter from the solution with benzin, a portion was precipitated by lead acetate. The precipitate did not behave as lead malate when heated under water, but was mostly soluble in solution of ammonium chloride. Another portion of the solution gave no precipitate with calcium sulphate, but with an excess of calcium hydrate, a white precipitate was produced. This precipitate was soluble in a solution of potassium hydrate, and the solution formed a gelatinous precipitate on boiling which was partially dissolved again after the solution was pooled, thus proving the presence of tartaric acid. The precipitate was also soluble in acetic acid.
The filtrate from the lime precipitate was boiled, when a slight precipitate was formed insoluble in solution of potassium hydrate, showing the presence of citric acid. On adding solution of potassium permanganate it was not decolorized until upon the addition of potassium hydrate when the color was slowly changed to green.
The seeds, after having been dried, were reduced to powder, and macerated with benzin at a warm temperature for several days, then packed in a percolator and exhausted with benzin. The powder was dried and a portion of it was digested for several days in alcohol, packed in a percolator and exhausted with alcohol. In like manner they were successively exhausted with water, with a very dilute solution of potassium hydrate and with water acidulated with sulphuric acid.
The benzin product from the seeds was an amber-colored oil, which oil was purified by washing with water and afterwards with chloroform. It was then found to weigh 7.25 per cent. of the weight of the seed extracted, and to be of specific gravity .926. It possessed a slight disagreeable odor and insipid taste, insoluble in alcohol or chloroform, soluble in benzin and ether.
Treated with 25 per cent. nitric acid and a strip of copper turnings, the mixture assumed a red-brown color, but after a day became partly solidified and lighter brown. A quantity of the oil was saponified by potassium hydrate; the solution precipitated by and washed with sodium chloride, and the soda soap decomposed with hydrochloric acid. The fat acid was odorless and tasteless, of a translucent milky color and with slight acid reaction. Its lead salt seemed to be but slowly soluble in alcohol and insoluble in ether. The mother liquor of the soap contained glycerin.
The alcoholic percolate of the seeds was nearly colorless and inodorous and of but slight taste foreign to alcohol and gave evidence of the presence of glucose. It was evaporated to dryness, thoroughly washed with water, and with chloroform to remove a greenish extractive matter, when a red-brown resinous residue was left having a slight disagreeable odor, a slight nauseous, disgusting taste, fusible at 100°C., insoluble in benzin, chloroform or ether, but soluble in alcohol, diluted alcohol and carbon disulphide.
The percolates with cold and hot water contained glucose, starch, and albumen; but neither a glucoside nor an alkaloid could be detected.
The dried gum was found to be entirely insoluble in water or alcohol, but in the presence of an alkali it became soluble.
Of the powdered seeds extracted with benzin 75 grams were boiled with several portions of water until the water from them gave no coloration with iodine; the starch was converted into sugar; this was estimated by Fehling's solution, and the starch calculated from it giving 3.95 gram or 5.268 per cent.
The residuary powder was now boiled with diluted sulphuric acid for several hours, when the liquid contained glucose and on concentrating it transparent rhombic crystals were formed, which were insoluble in alcohol or ether, readily soluble in boiling water, and this solution was not precipitated by ammonium oxalate.
In reviewing the results of my work we find in this unpretending and unnoticed plant, not only a remarkable and peculiar histology, but interesting constituents which surely seem to possess sufficient individuality to deserve a closer investigation.