III.

WHEAT.

1. STRUCTURE.

51. Relationships.-Wheat belongs to the family of true grasses (Gramineae). The Gramineae are characterized by having hollow stems with closed joints, alternate leaves with their sheaths split open on the side opposite the blade. Wheat is included under the tribe Hordeae, in which the spikelets are one to many-flowered, sessile and alternate, thus forming a spike. (59) To this tribe belong also rye and barley, as well as the cultivated rye grasses (Lolium perenne L. and L. itali cum Beauv.). This tribe also includes some troublesome weeds. Couch grass (Agropyron repens Beauv.), a perennial, was formerly included in the same genus as wheat. Because of its underground stems, or rhizomes, couch grass is difficult to eradi

cate and thus becomes a very troublesome weed in cultivated fields. Darnel (Lolium temulentum L.) is common in wheat fields in Europe and on the Pacific coast in this country. A related species (L. remotum) occurs in flax fields.

52. Roots. When a grain of wheat germinates, it throws out a whorl of three seminal or temporary roots. The coronal or permanent roots are thrown out in whorls from the nodes. The distance between the temporary roots and the first whorl of permanent roots will depend somewhat upon the nature of the soil, but principally upon the depth of planting. The depth at which the first whorl of permanent roots occurs will vary with the

soil, but is usually about an inch from the surface, irrespective of the depth of the grain or of the temporary roots. There is nothing in the nature of a tap root in any of the grasses such as is found in the legumes. Any node under the soil, or even near the soil, may throw out a whorl of roots. When wheat is planted under ordinary field conditions the roots curve slightly outward and then descend almost vertically. The more unoccupied soil about a wheat plant the more the roots curve outward. As soon as the available surface soil is occupied the roots descend. An abundance of roots has been observed at a depth of four feet, and under favorable conditions they doubtless go much deeper. Schubart traced the roots of a winter wheat plant seven feet deep.1 Webber found that if the roots of one wheat plant were placed end to end they would reach 1,704 feet. Near the surface the roots branch and re-branch abundantly, filling the soil with a mass of roots, the ends of which are covered with root hairs. The Minnesota Station found about eight branch roots to the inch on the main roots to a depth of eighteen to twenty inches, varying in length from one-half inch to twenty inches. Below this distance few or no branches were found, suggesting that the purpose of these deep roots was to secure water.3

53. Culms. Like the majority of the plants of the grass family, wheat has usually hollow culms, but in some varieties this space is more or less filled with pith. The greatest variation is found in the upper internode, which should be examined in describing a variety. The walls of the culm also vary in thickness, and the surface varies in color, and may be whitish, yellow, purple or brownish. Just below the spike the surface of the culm is more or less furrowed. The length varies with type and variety. The same variety is variable on different soils, with different fertilizers, and in different seasons. The variation in length of stem and yield of straw is greater than in size or yield 1 Agricultural Botany. M. C. Potter. p. 170.

2 Ibid.

3 Minn. Bul. 62 (1899), p. 405.

of grain. It would not appear that there is any necessary re lation between the length of straw and the yield of grain, although, all other things equal, the longer the culm, the greater the yield of grain. The club varieties of wheat grow about two feet high, while common wheat varieties grow to a height of from three to five feet; probably the average height is four feet.

The length of the culm has an important influence upon the liability to lodge, and also influences the ease of harvesting. It seems probable that the yield of straw may affect the loss in soil fertility, especially if the straw is not returned to the soil. On land of good average fertility the Ohio Station produced ninetyfive pounds of straw for each bushel of wheat during a period of ten years' continuous culture without fertilizers; 115 pounds per bushel where a complete commercial fertilizer was used, and 111 pounds per bushel where farm yard manure was used annually.1

During the early growth of wheat the nodes are very close together and consequently the plant consists principally of leaves. This condition obtains until the wheat begins to shoot, which consists of the lengthening of the internodes and the pushing up of the spike. The leaves which were formerly bunched together within a foot of the surface of the ground are now scattered along the culm, and in field conditions are comparatively scanty, and apparently inactive, except near the top of the culm, even at the time of blossoming. As the weight of the starch, as well as other material laid up in the seed subsequent to this time, is large, and as no starch is found laid up in the leaves prior to this time, as in some other plants, the question has been raised as to the ability of the active leaves to elaborate so much starch in so short a time. In fact, during the latter part of the ripening period only the glumes and the upper part of the stem remain green. Investigations indicate that the glumes do not have the capacity to form carbohydrates from the air, while the upper part of the stem has such power.2

1 Ohio Bul. 110, p. 47.

2 Ann. Agron. 28 (1902), No. 10, pp. 522-527. (E. S. R., Vol. XIV, p. 634.)

Leaves.

54. -There are four parts of the wheat leaf that should be distinguished: (1) the blade, which may vary in length and width, in shape, in smoothness, and in the prominence of its veins; (2) the sheath, which, as in all plants of the family, clasps the stem tightly and

is split down the side opposite the blade; varies in growing plant from green to purple; (3) the ligule, a thin, transparent tissue borne at the juncture of the blade and sheath and clasping the culm, varying in length from .07 to .I of an inch (1.7 to 2.5 mm.'); and (4) the leaf auricle, thin projections of tissue, outgrowths from the base of the leaf blade varying in color and hairiness.

55. Tillering.-Inasmuch as buds form in the axis of the leaves, by covering with earth, both roots and culms (branches) will form at any node upon the culm. Ordinarily, however, branches form only at the lower nodes. The number of branches which can form from a single culm is necessarily limited, but each branch may produce a limited number of branches and these branches in turn other branches, so that under favorable conditions several dozen culms and consequently spikes may be produced from a single seed. This is known as tillering and is one of nature's methods of giving the plant power to adapt itself to its environment. Under ordinary field conditions only a comparatively few culms form, but 1 The Description of Wheat Varieties. By Carl S. Scofield. U. S. Dept. of Agr., Bureau of Plant Ind. Bul. 47, p. 12.

at least fifty-two spikes have been produced from a single seed.

The "stand" of wheat may be materially affected by the amount of tillering, and, therefore, a study of those conditions which will promote tillering is advisable. On the other hand, it is probable that the best yields are not obtained where too much tillering is encouraged through thin seeding.

"In starting from the seed the stem soon begins to branch. The first leaves which are sent up seem to be a temporary set of organs designed to quickly reach above the soil, that the plant may be supplied with green cells in the sunlight. These leaves form what appears to be the primary shoot of the plant, and spring

A stool of wheat.

from the stem near the seed. They are found to be dead in the spring, along with the germ whorl of roots, in case of several varieties of winter wheat. At the same point where these first leaves arise another stem, apparently a rhizome, branches off from the primary stem. This rhizome has an internode quite unlike all the other lower internodes, not even covered by the sheath of a leaf, and extending about half way to the surface of the soil. In case the seed is planted two inches deep this rhizome is about one inch long. At the top of this internode a joint bears a leaf, and a few other joints follow at very short intervals, each having a bud in the axil of its leaf." 2

56. The Organs of Reproduction.The flower of the wheat plant has three stamens. The anthers are attached to the tapering end of the thread-like filaments below the middle. As the flower opens the filaments rapidly elongate, pushing up and outside of the glumes the anthers which previously were closely packed about the ovulary. The attachment of the filament to the anther is such that the anther suddenly upsets and the pollen falis out of

Culms are from a single seed originally at a. One-third natural size.

1 Neb. Bul. 32, p. 91.

2 Minn. Bul. 62 (1899), p. 407.

8 NOTE: The word ovulary is here used in its proper sense, instead of the term ovary which is so often incorrectly used.