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the adults cannot be afforded. Indeed the number of sires that are to be found in the upper end of the curve is so small that the sires are apt to be but little if any better than the average. In the breeding of animals in practice it is the few inferior animals represented by the lower end of the curve that are discarded. In the case of plants, however, embryo plants (seeds) are produced in such abundance and at so small expense that only the few at the upper end of the curve which are distinctly superior need be saved. Instead of discarding the poorest ten per cent, as in the case of animais, only the best five, or even one, per cent may be saved in the case of plants.
47. TO DEMONSTRATE THE LAW OF VARIATION FROM TYPE.—Take one hundred ears of maize of one variety. Take weight of each ear in grams, or ounces, and mark with gum label. Arrange ears in order of weight. Furnish each student with a sheet of cross section paper, five inches square, with twenty sections to the inch, or five by ten inches, ten sections to the inch, and have each plot the curve indicated by the weight of the hundred ears. If necessary to save time, the instructor may have ears weighed and marked in advance of the class exercise. Variations in the length of one hundred ears may be shown in the same way.
Variation in the weight of grains of wheat may be shown if facilities for accurate weighing are at hand. The larger the number of grains used the better.
48. ORGANS OF REPRODUCTION.-In order to become familiar with the floral parts of wheat and other cereals, furnish each student with several heads of wheat in different stages of inflorescence:
1. Describe ovulary and state changes in size at different stages of maturity.
2. Describe stigmas, state number of styles and position at various stages of maturity.
3. Describe length and position of filaments at different stages of maturity and note manner and mode of attachment of filament to anther.
4. Describe method by which anthers open and discharge their pollen. Describe the pollen grain.
For a portion of this work a high power microscope will be desirable. A twoinch, two-thirds-inch and one-sixth objectives will be found suitable. With a large class specimens may be prepared by the instructor and placed under one or more microscopes and each student allowed to inake examination by turn.
To show that rye is cross-fertilized, while wheat is generally self-fertilized, a similar study of rye may be made. The large anthers and abundant pollen of the rye will be found to be the most striking contrast.
49. TIME AND MANNER OF BLOOMING. — The student may be required to watch the opening of the wheat flower and the discharge of the pollen. Hays has shown that this whole process may take place in less than an hour in spring wheat and that it usually occurs in the early morning hours.
4-40 AM 4-43 A.M 4-45 AM 4-47 AM 4-55 AM S-08 AM 5-15 AM. 5-18 A.M.
The opening of wheat flowers. (After Hays.) 50. COLLATERAL READING.-Selection and Its Effect on Cultivated Plants. Henry L. De Vilmorin. Experiment Station Record, Vol. XI, pp. 3-19.
Plant Breeding. Willet M. Hays. Division of Vegetable Physiology and Pathology, U. S. Department of Agriculture, Bul. 29, pp. 7-24.
The Station for Plant Breeding at Svalöf, Sweden. By David G. Fairchild. Experiment Station Record, Vol. XIII, pp. 814-819.
I. 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) Cross section of a grain of wheat through
occurs in flax fields. embryo showing tips of three rootlets before germination. (From microphoto. 52. Roots.—When a grain of graph by Rowlee.)
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.? 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.S
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 cr 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.
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 III pounds per bushel where farm yard manure was used annually.'
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.)