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to 50 grains, are usually formed on a spike of wheat, the average length of which is between 3 and 4 inches. Humboldt said that in Mexico each spike of wheat averaged 90 grains, though some had as many as 160. Mummy wheat has been observed with ears containing nearly a dozen branches. There are 150 grains in one ear, and as many as 60 ears from one seed. Wheat has the advantage of extreme diminution of the number of seeds to each flower, giving richness in starch and gluten, combined with the advantage of numerous flowers on each plant, giving many seeds. The Wheat Kernel is a dry, indehiscent, unilocular caryopsis. It is oval in shape, and has the appearance of being folded upon itself from two sides. A ventral crease marks the coming together of the two folds. At the base of the berry opposite the crease is found the embryo, germ, or chit. At the apex is a collection of minute hairs. The entire grain fills from 20 to 30 cubic millimeters of space, of which at least thirteen-fourteenths are occupied with the starchy endosperm. The latter al- || most surrounds the embryo, and its cells are very irregularly shaped. The embryo is composed of the absorbent organ (scutellum), and the miniature first leaves and roots. It forms about 6 per cent of the wheat kernel. oThe endosperm and embryo are com-o.o.o.o.o.o. rletely enclosed by a single layer of § :li: #".;; aleurone or gluten cells. The weight of bran; ; and&###$! this layer is 8 per cent of that of the ****P**** whole grain. The next covering is a single layer of collapsed cells, known as the tegmen. This is again surrounded by a third envelope, the testa, or episperm, which contains the greater part of the coloring matter of the grain. This coloring matter is of two kinds, one a palish yellow, and the other an orange yellow, and the degree in which one or the other predominates determines whether the wheat is known as white, yellow or red. The three layers just described constitute the envelope of the seed proper. They in turn are again inclosed by the pericarp, which is also composed of three layers, all colorless. The exterior of these three membranes, the cuticle, is easily removed by rubbing. Then come two layers of cellular tissue, the epicarp (from which spring the hairs above mentioned) and the endocarp. The tegmen and testa form about 2 per cent of the weight of the grain, and the pericarp forms fully 3 per cent. Thus the bran forms at least 13 per cent of the grain. Germination.—The three conditions essential to the germination of wheat are moisture, warmth and oxygen. In the absence of any one of the se the process will not begin, or if it has be gun it will cease. Johnson defines the period of germination as lasting from the time when the
Cro ti f in of wheat on the left. (Fro root let becomes ss, section of grain of wheat on the Ieft. m ...:...: o by Tolman.) , Transverse section, visible until the on the right, of an unripe grain enlarged about 100 stores of the times from drawing by Bessey. 1 o wall or pericarp; 2, outer integument; 3, "inner "...i. mother seed are
remains of nucellus; 5, aleurone cells; 6, starch ce exhausted and the young plant is wholly cast upon its own resources. At 41° F., the time required for the rootlet to appear in wheat is about six days, which time corresponds to the more general idea of the period of germination. At 51° this time is shortened about one-half. The time required for the completion of germination is 40 to 45 days at 41 to 55° and 10 to 12 days at 95 to 100°. The lowest temperature at which wheat will germinate is 41°, the highest 104°, and that of most rapid germination, 84°. This is according to Johnson. Other authorities claim that wheat will germinate and grow on melting ice. It has also been said that it does not germinate successfully at a high temperature, and consequently should not be sown until cool weather in southern climates. Dissolved salts seem to aid germination under ordinary field conditions. In germinating, wheat absorbs from five to six times its
weight of water. It loses 1.5 per cent of its own weight in 24 hours, 6.7 per cent in 90 hours, and 11.8 per cent in 144 hours. Besides the loss in weight, marked chemical changes take place which greatly decrease its value for bread baking purposes, and probably also as a food for stock. Great loss may thus be occasioned by the sprouting of wheat in field, shock, stack or bin. Experiments indicate that sprouted wheat will regerminate and form healthy sprouts until the stem (plumule) has reached a length of 34-inch in the first germination, and an average of 80 per cent of all sprouted wheat with the length of the stem not exceeding 1/2-inch will again germinate.” Stooling or Tillering.—Wheat, like other cereals, has the characteristic of throwing out side shoots after the plumule has appeared above the surface. These branches or culms may form at any node covered with soil. The number of such stalks from one seed varies much with conditions. There are usually at least six, but there may be from two to several dozen in extreme cases, 52 spikes having been observed. As a rule, the more favorable the conditions for plant growth, and the thinner the wheat is on the ground, the more it tillers. Cool weather during early development may result in a long period of subsequent growth which encourages tillering. Time of seeding a Żlso also has great influence, for late sown wheat may not have time to stool. The habit varies quite materially in different varieties. While thinner sown wheat may tiller more, a greater amount of seed per acre often increases the To...o. yield, even though there are fewer stools. A logo seed origiPliny is said to have declared that it was not y at uncommon in northern Africa and in Italy to find from 200 to 400 stalks of wheat growing from a single kernel. Humboldt put on record that in Mexico each grain of wheat produced 40 to 70 stalks. It is probable that each of these men was seeing with the eyes of an enthusiast. The Growth of a Wheat Plant is the aggregate result of the enlargement and multiplication of the cells which comprise it. Generally cells reach their full size in a brief time, and continuous growth depends mainly upon the constant and rapid formation of new cells. The essentials to growth are light, air, moisture, heat and food. In the absence of any one of these, the plant dies, and in their disproportionate combination, growth is sickly. In germination, food is furnished by the seed, and light is not essential. Over light man has no control. He can increase the amount of air that has access to the plant by loosening the soil around its roots. An adaptive control of heat is exercised by sowing during the warm season. By selecting soils, fertilizing and changing existing foods from unavailable to available forms, food can in a great measure be regulated, and water, acting as a solvent and vehicle, can be very largely regulated as to amount by drainage and irrigation. That the growth and multiplication of cells involves a migration of material within the plant has long been recognized. In wheat, as in many other plants, there is a comparatively large development of roots soon after the first leaves appear. Only some low-lying leaves are put forth while the great complex of roots is being formed. In a wheat plant only 23 days old, the roots had penetrated the soil over 1 foot in depth. When the system of roots has been formed, the stalk suddenly shoots up almost to mature stature. Perhaps the roots are completely developed by the time that the formation of grain has begun.
* Rept. N. D. Sta., 1901, p. 107.
The leaves of the wheat plant, with their chlorophyl cells, have been considered as little laboratories elaborating vegetable matter. Under the influence of light they are able to extract carbonic acid from the atmosphere. This acid is one of the raw materials of these little factories. They decompose it, eliminate the oxygen, and from the residue they manufacture sugar, cellulose, straw-gum, vasculose, and all the termary matters composed of carbon, oxygen and hydrogen. A perfect system of canals penetrates every part of the plant. These canals are filled with water, which enters at the roots, for leaves do not absorb water to any appreciable extent, and is in constant motion until it is exhaled from the leaves. During one hour of insolation a leaf of wheat exhales an amount of water equal to its own weight. Upon these highways of moving water are borne raw materials destined for the little cell factories, such as nitrates, phosphoric acid, potash and
silica. They, too, are reduced. If there is an abundance of rain, the cells continue work long, elaborate much vegetable matter, and the plant grows. If the water supply is insufficient and the soil parsimonious, this prodigious consumption cannot be supplied, and dessication of organs takes place. This begins in the oldest leaves, and nearly always the little leaves at the base of the stem become soft, flabby, and withered. Analyses have been made which show that these leaves let escape some nitrogenized matter, phosphoric acid and potash, which they contained when living, green and turgescent. Thus the closing of one of these groups of little cell factories by the dessication of a leaf is a very important process to the plant, for less vegetable matter is elaborated than if it had continued its work. In dry years a shortening of the stems and a comparatively small amount of straw results. The dying of leaves involves not only the closing of these workshops, but the transportation of much of the finished product stored in them. Metamorphosis of the nitrogenized matter which forms the protoplasm, the living part of the cell, takes place, and it assumes an itinerant property which enables it to pass through membranous walls and migrate over the liquid highways to new leaves. With it are carried phosphoric acid and potash. Some of the elaborated material is thus continually being transported from lower to upper leaves during the entire period of vegetation. Flowering takes place when enough material has been elaborated to nourish the appearing seeds. This migration of substance can take place only when there is plenty of water, and the crop fails when it is too dry. Too much water is also injurious, for it causes a tendency to keep up growth indefinitely. The Minnesota station found that the wheat plant produced nearly one-half its dry and three-fourths its mineral matter by the end of 50 days. This included 75 per cent of the potash, 80 per cent of the phosphoric acid, and 86 per cent of the nitrogen. At 65 days, 65 per cent of dry and 85 per cent of mineral matter had been produced, as well as most of the fiber, which suffered a loss after 81 days. Compared with the processes observed in nitrogenized matter, phosphorus and potash, the * Minn. Bul. 29. pp. 152-160. -