70. Gluten.-Wheat flour has the property in common only with rye flour of forming a dough when mixed with water which on leavening and baking produces a porous bread. This is due to the gluten which imprisons the carbonic acid gas caused by the fermentive action of the yeast. The gas expanding during leavening and during baking causes the bread to become

porous.

Gluten is a mixture of gliadin and glutenin and may be obtained in a crude state from wheat meal or flour, by washing the dough made by kneading the meal with water, which removes starch and other non-gluten compounds. Moist gluten contains about sixty-six per cent of water and certain other impurities which are in fairly constant proportions in different samples. A good gluten has a light yellow color, is tenacious and elastic, while poor gluten is dark in color, is sticky but not elastic.

“The gliadin with water forms a sticky medium, which by the presence of salts is prevented from becoming wholly soluble. This medium binds together the particles of flour, rendering the dough and gluten tough and coherent. The glutenin imparts solidity to the gluten, evidently forming a nucleus to which the gliadin adheres and from which it is consequently not washed away by water. Gliadin and starch mixed in the proportion of 1:10 form a dough, but yield no gluten, the gliadin being washed away with the starch. The flour freed from gliadin gives no gluten, there being no binding material to hold the particles together so that they may be brought into a coherent mass.

"Soluble salts are also necessary in forming gluten, as in distilled water gliadin is readily soluble. In water containing salts it forms a very viscid, semi-fluid mass, which has great power to bind together the particles of flour. The mineral constituents of the seeds are sufficient to accomplish this purpose, for gluten can be obtained by washing a dough with distilled water."

The amount and quality of gluten-especially the latter-is what gives the flour its baking qualities. The quality of the gluten is due in part at least to the proportion of gliadin and glutenin. M. E. Fleurent states that the most favorable ratio of glutenin to gliadin is twenty-five of the former to seventy-five of the latter. He gives analyses of two varieties which are in the ratio of 23: 77 and 30: 70 respectively, and suggests that

the breadmaking value of the flour may in such cases be increased by mixing in proper proportions the wheat or the flour made therefrom.1 Snyder states that the most valuable wheats for breadmaking are those in which eighty to eightyfive per cent of the protein is gluten and the gluten is composed of thirty-five to forty per cent glutenin and sixty to sixty-five per cent gliadin. He reports a variety of wheat from India with a ratio of 27:73 and one from the Argentine Republic with a ratio of 58:42. The value of a flour depends, therefore, more relatively upon the quality of the gluten than upon the per cent of the nitrogenous compounds contained.

2

71. GLIADIN.-With water containing salts or mineral matter gliadin is a plastic substance which may be drawn out into sheets or strings. By proper chemical manipulation it may be reduced to a snow-white powder. When distilled water is added to this powder it becomes sticky, but if a ten per cent solution of salt (sodium chloride) is added, it is non-adhesive, although plastic. Gliadin is soluble in distilled water, very soluble in seventy to eighty per cent alcohol, but is insoluble in water containing salts or in absolute alcohol. It is soluble in dilute acid and alkalis and may, therefore, be soluble in wheats that have undergone fermentation.

72. GLUTENIN.-Is the proteid which is left after dissolving the gliadin from the gluten with dilute alcohol. It is distinguished from gliadin by its lesser solubility, its darker color, and by being non-adhesive and non-plastic. It is insoluble in water, saline solutions and dilute alcohol, but is soluble in dilute acids and alkalis, from which it may be precipitated by neutralization. 3

73. Relation of Weight Per Bushel to Nitrogen Content.The usual and commercial standard of quality in wheat is the weight per bushel, high weight being associated with qualities desired by the miller. The following table gives the results of eight favorable seasons for wheat and eight unfavorable seasons with three conditions of fertility at Rothamsted:*

1 Compt. Rend. Acad. Sci., Paris, 126 (1898), No. 22, pp. 1592-1595.

2 The Chemistry of the Wheat Plant, pp. 276-277.

3 The Proteids of the Wheat Kernel. By Thomas B. Osborne and Clark C. Voorhees. Am. Chem. Jour. XV (1893), pp. 470-471.

4 Lawes, Sir J. B., and J. H. Gilbert. On the composition of the ash of wheat, grain and straw, grown at Rothamsted in different seasons and by different manures London (1884), pp. 105.

It will be seen that in seasons unfavorable for the yield the weight per bushel was light but the nitrogen content as well as the ash content was high, and on the other hand that in seasons of favorable growth the weight per bushel was high and the nitrogen and ash content were low. In these cases, covering a series of years and several conditions of fertilization, high weight per bushel was associated with large percentage of starch. Lawes and Gilbert conclude that "High percentage of nitrogen is by no means a characteristic of the wheats held in highest estimation either by the miller or the baker; and that so far as both the baker and consumer are concerned the condition of nitrogenous matters is of more importance than their total amounts. Comparing one description of wheat with another, the one with a relatively high percentage of nitrogen may be better, provided the grain be at the same time fully ripened and not too horny. But when the percentage exceeds a certain limit, the grain is generally either too hard, or there is deficient storing up of starch and an unfavorable condition of the nitrogenous substances."

74. Influence of Environment on Composition of Grain.-En vironment is a combination of influences of which the following three are the most important:

2. Soil, including fertilizers of all kinds.

3. Culture, including preparation of seed bed, time and method of seeding and quantity of seed, etc.

It has been shown that the composition of the wheat grain varies in different localities when grown from seed of a common origin. For example, Richardson found that the per cent of protein in a number of varieties of wheat was considerably higher when grown in Colorado than when grown in Oregon. He also found that the grains of wheat were much larger when grown in Oregon than when grown in Colorado. Deherain makes a similar observation with regard to the influence of different seasons. High temperature during July (in France) increased the per cent of protein but diminished the yield so that the amount of the protein was no greater than under normal conditions. The high per cent of protein in the hard spring wheats of the northwest is likewise attributed to the arrested development of the endosperm or starchy portion of the grain.

Richardson attributes the variation in the per cent of protein to the differences in soil and attributes low per cent of protein found in some American wheat to a deficient supply of nitrogen. Lawes and Gilbert state that the low percentage of nitrogen is more probably due to the enhanced formation of starch under the influence of high ripening temperatures, and that, comparing the grain grown from the same description of seed but on different soils, or in different seasons, high percentage of total nitrogenous matter is almost invariably coincident with inferior ripening. Wiley attributes the variation in per cent of protein to climatic conditions, but attributes variation in the ash occurring in the same varieties of wheat to the soil and fertilizers.1 1 Influence of Environment on the Composition of Plants. By H. W. Wiley Yearbook, Dept. of Agr., 1901, p. 306.

Carleton believes that localities with black soils (high in organic matter) and extreme climatic variations are most favorable for the production of high protein content. William E. Edgar says:

"Gradually as the northwestern States have become cultivated the original hard wheat has grown scarcer. Wheat raised on virgin lands has a peculiar strength lacking in that produced in older fields. It is capable of improving the character of other wheat blended with it when the mixture is made into flour." 1

Lawes and Gilbert, in an elaborate series of analyses of wheats grown on unmanured and variously manured plats during twenty seasons, have shown the variation in composition of wheat to be much more influenced by season than by manuring. There was very little variation in the mineral composition of the wheat grain accorded to manuring except in cases of abnormal exhaustion. Commenting upon the significance of the facts presented, the authors say:

"The character of development of a crop left to ripen, depends very much more upon season than upon manuring. Indeed, if one crop (of wheat for example) grows side by side with another of exactly the same description, but yielding under the influence of manure twice the amount of produce, and both under such conditions of season that each fully and normally ripens, the composition of the final product, the seed, will be very nearly identical in the two cases. In other words, there is scarcely any difference in the composition of the truly and normally ripened seed. But, as variations of season affect the character of development, and the conditions of maturation, there may obviously be, with these, very wide differences in the composition of the product. The wide range in the composition of the ash of the grain, which the table shows according to season, represents in fact a corresponding deviation from the normal development." 2

The climatic condition which seems most uniformly to affect the composition of the grain is the length of season of growth. The shorter the season of growth, the higher the percentage of protein and the lower the percentage of starch. Doubtless the shorter the season of growth, the smaller the grain.

It does not follow that strains may not be selected which will contain high per cents of protein and at the same time produce more protein per acre, although the facts stated above suggest that difficulty may be found in doing so.

1 The Story of a Grain of Wheat, p. 126. New York, D. Appleton & Co., 1903. 2 Lawes and Gilbert on the composition of the ash of wheat-grain and wheat straw, p. 8.