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Leaves.—When the internodes lengthen and the spike pushes upward, the wheat is said to shoot. Previous to this, the nodes are so close together that the plant seems to consist almost entirely of leaves. There are four principal parts to the leaf: The blade; the sheath, which clasps the stem and is split down the side opposite the blade; the ligule, also clasping the culm, and located where the blade and sheath join; and the leaf auricle, thin projections growing from the base of the blade. The first leaves of the wheat plant and the germ whorl of roots do not live through the winter in some varieties.
The Flower of Wheat is constituted collectively of the organs of reproduction, together with the two inclosing chaffy parts. The inner of these two parts is known as a palea, while the outer and lower one is the flowering glume. The latter often bears a long appendage, characteristic of bearded wheat. These awns or beards vary greatly in length even in the same spike, and in some varieties are deciduous upon ripening. Their color varies from light yellow to black.
wi?era?nl0oVar?^U^°"ti8° The Spikelets.-Each consists of from rthebH^at0time°ofetetwo to five flowers encased within two
ering;C, flower before open-hard oval chaffy coverings called outer ing, o, anthers, /, filament, , _ * ° . ,
I, iodicule; D, flower about glumes. In common wheat each
toopen' spikelet generally matures two, and
sometimes three, grains. The glumes vary greatly in form, color and size. The stem orrachis of the spike is of a zigzag form. On each of its joints or shoulders sits a single spikelet, attached by an exceedingly short rachilla. Arranged alternately on the stem, with flat sides toward the center, the spikelets usually give the head of wheat a square appearance when viewed endwise. Viewed from the side, the spike may be straight or curved; it may have uniform sides, or taper toward both ends, or only toward base or apex; or it may be clubbed at either end. The filling of the spikelets has much to do with the appearance of the spike, which varies much in different varieties. There is also great variation in compactness. Fifteen to twenty fertile spikelets, containing from 30 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 almost 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.
The endosperm and embryo are com- J^ff &g&*!
rletely enclosed by a single layer of gluten cells: tf, Inner coat of
. , ,, rr.7 . . „ "fan; e, coloring matter of
aleurone or gluten cells. The weight of bran;/ and a, outer coats of this layer is 8 per cent of that of the bran; A, epKTermisof kernel.
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 these the process will not begin, or if it has begun it will cease. Johnson defines the period of germination as lasting from the time when the rootlet becomes Cross section of grain of wheat on the left. (From ,-„:i.i„ „„t;i iu» micro-photograph by Tolman.) Transverse section, »ls'oie until me
on the right, of an unripe grain enlarged about loo ctores
times from drawing by Bessey. 1, ovary wall or peri-'
carp; 2. outer integument; 3, inner Integument: 4, mother
remains of nucellus; 5, aleurone cells; 0, starch cells. , , ,
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 %-inch in the first germination, and an average of 80 per cent of all sprouted wheat with the length of the stem not exceeding V^-inch will again germinate.1
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 „ 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 yield, even though there are fewer stools. Pliny is said to have declared that it was not 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. "Kept. N. D. Sta_, 1901, p. 107.
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. 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 ternary 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