Life Sciences Commons^™

Major Changes In Grassland As A Result Of Continued Drought, J. E. Weaver, F. W. Albertson

Department of Agronomy and Horticulture: Faculty Publications

A comprehensive research on 135 large tracts of prairie was completed in 1933 after five years of study. These tracts were distributed over an area of 60,000 square miles, including the eastern one-third of Nebraska, the western one-third of Iowa, and adjacent areas in the four neighboring states (2). This investigation furnished the background for an understanding of the profound changes which have occurred during the several years of the great drought, which first became pronounced in 1934. The response of prairie to the drought of that year has been discussed (3). Likewise, a detailed account of the destruction caused …

Effect Of Frequent Clipping On Plant Production In Prairie And Pastur, J. E. Weaver, V. H. Hougen

Department of Agronomy and Horticulture: Faculty Publications

The degeneration of native bluestem prairies of eastern Nebraska occurs slowly under moderate grazing or slight overgrazing but within two to five years where overgrazing is pronounced. Although the changes in the plant populations are continuous until the soil is finally almost bare, for convenience of study they have been grouped into several more or less distinct stages (Weaver and Harmon, 1935). An intermediate stage in deterioration is indicated by a great increase in the abundance of bluegrass (Poa pratensis), blue grama grass (Bouteloua gracilis), or buffalo grass (Buchloe dactyloides), the latter especially on …

A Zygotic Lethal In Chromosome 1 Of Maize And Its Linkage With Neighboring Genes, R. A. Emerson

Department of Agronomy and Horticulture: Faculty Publications

A Bolivian maize

maize with mosaic red pericarp and cob, here designated by the symbol M-M, crossed with a local inbred strain of maize having white pericarp and cob, W-W, produced in F₁ 21 M-M and 28

W-W plants, not far from the I : I relation expected on the assumption that

the M-M parent was heterozygous for pericarp and cob color, M-M/W-W.

In F₂ and segregating F₃ cultures, however, there were 130 M-M and 64

W-W plants obviously a 2 : I instead of the 3 : I relation expected. Later cultures

increased these records to …

Root Distribution Of Trees In Relation To Soil Profile, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

One of the pronounced trends in American forestry during the past decade has been the development of a widespread interest in soils. As a consequence to the soil as a part of the environmental complex has been attributed much greater importance than formerly in forest production. In fact, the individual horizons of the soil profile are receiving attention each as a more or less distinct habitat of that highly organized body designated as soil. Just as soil scientists, until recent years, have given inadequate attention to the factor of vegetation in the constitution and development of soils, so too little …

Effects Of The Great Drought On The Prairies Of Iowa, Nebraska, And Kansas, J. E. Weaver, F. W. Albertson

Department of Agronomy and Horticulture: Faculty Publications

The response of prairie vegetation of eastern Nebraska during the great drought of 1934 has been described (Weaver, Stoddart, and Noll, '35). The purpose of the present study was to determine the results of the drought during the following year. The work has been extended to include the mixed prairie of west central Kansas.

Reports From "Drought Front" Tell State Or Vegetation, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

Development of the natural prairie vegetation is an excellent indicator of the intensity of drought. The extreme drought of 1934 left many bare areas in the grasslands and all but swept away most of the least drought-resistant species. The dry early spring and later summer of 1935 witnessed great increases in needlegrass, western wheat grass, and the invasion of a host of weeds. The favorable spring of 1936 promoted an abundant growth and emphasized the great changes in the prairie flora.

Relative Efficiency Of Roots And Tops Of Plants In Protecting The Soil From Erosion, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

Plant cover, soil and topography are the major factors concerned in the problem of erosion. During the earlier studies, conducted largely by engineers, chief emphasis was placed upon topography. Following extensive work by pedologists, it is now generally conceded that type of soil is an equally important factor. Intensive studies on the effect of plant cover reveal the extremely important role played by plants in holding the soil against the forces of erosion. In this preliminary account of the relative effectiveness of roots as compared to tops in holding the soil in place, the results are based on extensive experiments …

Role Of Fire In Pasture Management, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

The practice of burning grass is an old one. It was extensively used by the Indians to attract game animals in early spring and to facilitate hunting. It is also highly probable that a large portion of the prairie was burned periodically during very dry years from natural causes

Response Of The Prairie To The Great Drought Of 1934, J. E. Weaver, L. A. Stoddart, W. M. Noll

Department of Agronomy and Horticulture: Faculty Publications

Drought during the growing season of 1934 was the greatest ever recorded in the prairie region. It offered an exceptional opportunity to study the response of native plants to extremely adverse water relations. Measurements of the environmental factors of the prairie, in connection with various grassland researches, have now been completed, except for one year, for the seventeenth consecutive growing season. In a summary of findings at the end of twelve years it was stated that although periods of drought are liable to occur at any time, and especially after midsummer, yet only twice during these twelve years was the …

Relation Of Root Distribution To Organic Matter In Prairie Soil, J. E. Weaver, V. H. Hougen, M. D. Weldon

Department of Agronomy and Horticulture: Faculty Publications

Although the root distribution of the chief grasses and forbs of tall-grass prairie has been known for 15 years (18), no studies on the relation of root distribution to the organic matter in the soil have been made. In fact, so far as the writers are aware, few studies of this type have been undertaken in America. SPRAGUE (15), working in New Jersey, has attempted to correlate root occupation of the several soil layers with their specific soil properties. The grasses, chiefly Kentucky bluegrass and Colonial bent grass, were grown on a formerly cultivated soil of the gray-brown forest soil …

Measurement Of Run-Off And Soil Erosion By A Single Investigator, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

That run-off water and soil erosion have become problems of both local and national importance is widely recognized. In fact soil erosion over at least half of the United States has reached the proportions of a national menace. To study quantitatively the amount of run-off and erosion from different topographical areas and types of soil under various climates as well as the quantities of soil lost under different methods of cropping, terracing, etc., the government has established Federal erosion stations. These are located in various widely separated areas. The accumulated results obtained at these stations are now finding an important …

Stability Of Climax Prairie And Some Environmental Changes Resulting From Breaking, J. E. Weaver, Evan Flory

Department of Agronomy and Horticulture: Faculty Publications

Continued study of the great midcontinental grasslands of North America throughout a period of years has impressed the writers with the high degree of stability of the climax prairie. This phenomenon has been carefully considered in a study of the types of prairie in the Missouri Valley over an area of several thousand square miles centering in eastern Nebraska but including five neighboring states. Present studies on the deterioration of the prairie under the impact of grazing, and changes in edaphic and atmospheric environment with the breaking and cropping of the land have further emphasized the stabilizing influence of a …

The Prairie, J. E. Weaver, T. J. Fitzpatrick

Department of Agronomy and Horticulture: Faculty Publications

This research is the third of a series of investigations of the prairie. The first dealt with the environment of the prairie (Weaver and Himmel, 1931). The second was concerned with the ecology and relative importance of the dominant grasses (Weaver and Fitzpatrick, 1932). The present study treats of the structure of the vegetation in the several types of prairie, the secondary grasses, the ecology of the forbs, together with a general survey of contacts, invasion, and succession. These investigations have resulted from years of intimate association with the great grasslands of North America. They were made in an endeavor …

Relation Of The Differential Fertilization Genes, Ga Ga, To Certain Other Genes Of The Su-Tu Linkage Group Of Maize, R. A. Emerson

Department of Agronomy and Horticulture: Faculty Publications

The Ga, or “gamete” gene of maize can be studied only or principally by its disturbance of normal Mendelian ratios of contrasted characters differentiated by genes linked with it. The amount of this disturbance can be used as a measure of the intensity of linkage between Ga and other genes of the su-Tu group.

Disturbance of the 3:1 ratio of starchy, Su, to sugary, su, endosperm has been most studied. In one of the early papers on Mendelian inheritance, Correns (1902) reported that, although crosses between most starchy and sugary varieties gave an F₂ ratio of …

Effect Of Frequent Clipping On The Development Of Roots And Tops Of Grasses In Prairie Sod, Harold Biswell, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

A study has been made of the regeneration of bluestem grasses in ex- closures in continuously grazed native pastures. The persistence of remnants of the bunches or mats of sod in old pastures for a long period of years is of interest, as is also their gradual but slow rate of recovery under protection when they are greatly weakened. Even in low, fertile, well watered soil, a period of three or four years must elapse before such species as Andropogon furcatus and Sorghastrum nutans produce the usual abundance of flowers stalks and large quantities of viable seed. The first summer …

Root System Of Quercus Macrocarpa In Relation To The Invasion Of Prairie, J. E. Weaver, Joseph Cramer

Department of Agronomy and Horticulture: Faculty Publications

Invasion of trees into grassland is primarily a phenomenon of plant competition. It involves the relation of the invaded and the invader to light and other atmospheric factors of the habitat, both physical and biotic. But perhaps even to a greater degree the edaphic factors, and especially water in dry climates, are concerned. Consequently to understand the reasons for plant distribution and the changes resulting from natural successions, a knowledge of the parts of the plants underground and of the interrelations of the root systems is of fundamental importance.

The great tension zone or ecotone between the deciduous forest formation …

Ecology And Relative Importance Of The Dominants Of Tall-Grass Prairie, J. E. Weaver, T. J. Fitzpatrick

Department of Agronomy and Horticulture: Faculty Publications

This paper is the result of an intensive study of the vegetation of the prairie. The study extended over a period of ten years. It deals with the life histories, distribution, and relative importance of the dominant grasses in a central area of the tall-grass prairie. This area includes the grasslands of the western one-third of Iowa and those of approximately the eastern one-third of Nebraska. On the south it extends into Missouri and Kansas to the Kansas River. North- ward it includes a small portion of southwestern Minnesota and a larger one of southeastern South Dakota.

Indicator Significance Of Brush Lands For The Growth Of Western Yellow Pine, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

A study of unusual interest and significance in the application of ecological principles to the solution of an economic problem has recently been completed. It deals with the causes for the absence of western yellow pine in brush vegetation of various types that occur throughout the mountainous portions of northern Utah, eastern Idaho, and western Wyoming, and, in fact, form a much interrupted and fragmented belt whose center extends from the Gulf of California to west-central Montana. Many of these brush sites, especially in northern Utah and southern Idaho, lie immediately below the Douglas fir type (which is continuous) and …

The A Series Of Allelomorphs In Relation To Pigmentation In Maize, R. A. Emerson, E. G. Anderson

Department of Agronomy and Horticulture: Faculty Publications

Introduction ... 503

The allelomorph A^b ... 504

The allelomorph a^p ... 505

Dominance ... 508

Summary ... 508

Literature Cited ... 509

Who's Who Among The Prairie Grasses, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

For many years I have lived on the prairie, where I became familiar with the grasses. Each spring I have been delighted with their renewal of growth in watching the brown landscape of rolling hills become carpeted with green. Year after year, with the progress of the season, I have seen the changing aspects, which, with the coming of autumn, end in the wonderful coloration of the prairie grasses. But the prairie as a whole has seemed a somewhat elusive thing, difficult to visualize, not easy to describe, indefinite and extremely variable in its composition. This vagueness of understanding, I …

Underground Plant Development In Its Relation To Grazing, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

Grasslands or grazing lands are relatively dry lands. Drought, at least in the surface soil, is always imminent. The necessity for the seedling to make immediate and extensive contact with deeper, moister soil is apparent. The water relation is usually controlling, and the success or failure of the seedling largely depends upon its ability to develop an absorbing system adequate in extent and activity to furnish the necessary supply.

Alfalfa Production In A Grassland Climate, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

The importance of root extent and activities in relation to the supply of subsoil moisture has again been clearly demonstrated. In fact, it has been shown to be the chief problem in the continued production of alfalfa in a grassland climate.

Studies extending over a period of 15 years have shown that the native species of the tall-grass prairie never exhaust the water supply below that available for plant growth, except rarely in the shallower soil. The subsoil is always moist, and plants root deeply. Of 43 species typically representative of the flora, only 14 per cent absorb almost entirely …

Relation Of Increased Water Content And Decreased Aeration To Root Development In Hydrophytes, J. E. Weaver, W. J. Himmel

Department of Agronomy and Horticulture: Faculty Publications

The dependence of root development of most plants upon aeration is clearly shown by water-logging the soil. In a few days, the usual cultivated plants turn yellow, show wilting, and may ultimately die. If the water is kept well aerated, plants may survive though submerged for weeks. Exclusion of oxygen from the roots of most plants interferes with the respiration of the protoplasm of their cells. This results in the death of the cells and consequently the roots fail to function as absorbers for the plant (22).

Relation Between The Development Of Root System And Shoot Under Long- And Short-Day Illumination, J. E. Weaver, W. J. Himmel

Department of Agronomy and Horticulture: Faculty Publications

Relatively few investigations have been made to determine the factors which affect the relation of the growth of roots to tops. A more exact knowledge of the relations between aerial and subterranean plant parts and the degree to which these may be modified through cultural practices is of great scientific and practical importance. Extensive investigations have shown that plants exhibit marked specific and varietal differences with respect to relative development of roots when grown under the same environmental conditions. Intensive studies on the growth of wheat by Weaver, Kramer, and Reed (20) and of certain other plants by Crist and …

The Frequency Of Somatic Mutation In Variegated Pericarp Of Maize, R. A. Emerson

Department of Agronomy and Horticulture: Faculty Publications

Some years ago (Emerson 1922) the writer announced that in F₂ of

certain crosses of variegated with colorless pericarp in maize the heterozygous

individuals changed to self color more frequently than did the homozygous

individuals of the same cultures. No “explanation” of this phenomenon

was then apparent, but later results, though still far from affording

an adequate solution of the problem, have furnished at least a working

hypothesis. The original unpublished paper, with minor modifications,

is given below, under the heading. “Somatic mutations in heterozygous

and in homozygous variegated pericarp.”

Experimental Studies Of Cultivation Of Certain Vegetable Crops, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

For those who have an interest in the ecology of cultivated plants, Thompson's experimental studies on vegetable crops has a wealth of information. This memoir deals not only with the effect of cultivation on yield, but analyzes the several factors of soil moisture, soil temperature, and the production of nitrates as affected by cultivation, and the effect of weeds on these factors. Finally the root habits are studied, and a correlation is made between the root system and the response of the plant to cultivation.

Structure Of Texas Vegetation, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

In his studies on the structure of the vegetation of eastern Texas, Tharp has recently made a notable contribution to plant ecology. That unexplored vegetation has always had an irresistible attraction for botanists is well ex-emplified in the resume of studies of Texas vegetation. An adequate review of the earlier work is given. This work began even before the colonists declared their independence from Mexico. It includes the studies of Lindheimer, who was both a geographer and collector; deals with the numerous papers along broad ecological lines by Bray; and traces the studies to the recent analysis of the vegetation …

Crop Production In India, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

It is rarely that one finds a book on the subject of agriculture of such broad scope, fascinating interest, and so full of the applications of ecology and physiology as Howard's " Crop-production in India." In every chapter numerous problems of plant growth in relation to environment are brought before the reader in such a stimulating manner that one can scarcely conclude but that ecology will reach its greatest usefulness in the field of general agriculture. It is a book to which every student of environment should have ready access.

Some Ecological Aspects Of Agriculture In The Prairie, J. E. Weaver

Department of Agronomy and Horticulture: Faculty Publications

It is of more than passing interest that the cereal crops, namely: corn, spring and winter wheat, oats, barley, sorghum, and millet, have their center of greatest production in that portion of the United States originally covered by grassland. In fact, some are grown almost entirely in the grassland region, and other crops, as alfalfa and flax, which are similar in growth habits to wild legumes, wild flaxes, etc., growing among the grasses, also have their greatest acreage in grassland. Likewise, the largest areas of fruit production, including such tree fruits as apples, peaches, pears, and bush fruits as blackberries, …

The Segregation Of Carbohydrates In Crosses Between Waxy And Starchy Types Of Maize, T. A. Kiesselbach, N. F. Petersen

Department of Agronomy and Horticulture: Faculty Publications

The purpose of this paper is to report the Mendelian segregation of waxy and starchy carbohydrates in both the sporophytic and gametophytic generations of maize. This is of especial genetic interest because the counts of segregate waxy kernels have very commonly been short of the expected numbers, although this character appears to be a simple Mendelian recessive. Collins (1909) was the first to point out the physical difference in the endosperm of waxy and ordinary starchy varieties.

While the exact difference in their chemical nature has not been established, Weatherwax (1922) considered that the waxy carbohydrate was erythrodextrin because of …