The resistance for months to deterioration by microorganisms (in soil burial) of suitably acetylated fibrous cottons, some with only one-third of the hydroxyl groups substituted, depends upon the distribution of the acetyl groups as well as upon the total number of such groups present. Under usual conditions of acetylation, according to the literature, reaction takes place first in the amorphous cellulose, starting at the most accessible places. According to the present ex perimental acetylations and special dyeing tests, the reaction, which is probably confined at first to the amorphous cellulose, takes place along fibers in various segments and throughout cross sections rather than as a layer increasing in thickness from the surface inward. At one-third substitution the amorphous cellulose is converted to triacetate; the cotton fiber still contains about two-thirds of the original cellulose, which is present as crystalline material surrounded by acetylated cellulose. The swelling capacity of the cotton in water is greatly reduced. While the mode of attack by microorganisms is not completely understood, they apparently begin at the most readily accessible amorphous cellulose. From the literature and from the present experiments, protection by partial acetylation is believed to be due to the blocking of hydroxyl groups, the filling of spaces between chains in the amorphous cellulose, and the sup pression of swelling. It represents a general method of rendering cellulose unsuitable, or at least inaccessible, as a food for microorganisms. A relatively low degree of partial saponification may detract greatly from the rot-resistance of a well-protected acetylated cotton owing to the restoration of amorphous cellulose, with loss of blocking groups and a restoration of swelling capacity. Partial methylenation by treatment with formaldehyde may impart a moderate degree of rot-resistance, which seems best explained as being due to the suppression of swelling by cross linking. Formaldehyde-containing resins which impart rot-resistance apparently act similarly. The evidence obtained indicates that the amorphous cellulose is the part which is normally attacked, and that its ability to swell in water may be a more important factor in microbiological attack than is commonly recognized. The use of dyeing has been exemplified for qualitative tests to supplement other evidence regarding substitution and the composition and properties of substituted cottons.

Exposure of cotton in the field to wet weather following normal opening of the boll and fluffing of the fiber resulted in increases in the pH of aqueous extracts of the fiber, as determined by methods herein described, from a level in the general range of pH 6.3 to 7.3 for the un- weathered fiber to progressively higher values. The maximum pH attained was in the range of 9.5 to 10.0, and was sometimes reached within a period of 5 days. Cotton fiber subjected to wet weather during the process of boll opening, with the consequent unfluffed and darkened appearance characteristic of "fungus tight-lock" and "boll rot," had pH values ranging from 5.3 to 9.7. In the case of the common Diplodia tight-lock, serious fiber weakening and fiber disintegration were accompanied by pH values from 5.6 to 6.8. Pure-culture laboratory tests involving inoculation with fungi and humid-atmosphere incuba tion of fiber and unbleached cotton fabric, followed by pH determinations, indicated that several microorganisms, including certain types of common occurrence on field-weathered cotton, may bring about very rapid pH increases of the same general magnitude as those observed with fiber exposed to humid weather in the field. Both cellulose-decomposing and noncellulose-decom posing fungi brought about pH changes, which were upward in direction for 24 of the 27 isolates tested. Once high pH values were attained, no subsequent decrease in pH occurred dur ing incubation periods of 4 weeks' duration. On water-saturated cotton fiber mats, certain com mon bacteria and a common yeast produced pH increases. Data suggest that increases in the aqueous-extract pH of cotton fiber may be caused by the decomposition of malic or other organic acids in the fiber by microorganisms. Fiber which had attained a high aqueous-extract pH during weathering exhibited a decline in this value with time in storage. In tests here reported, the higher the original pH of the sample, the more rapid was the initial rate of decline in pH during storage. A decline in pH may occur also while the fiber is still on the plant in the field. The pH test appears to offer promise as a rapid method of fairly wide applicability for de tecting the growth of microorganisms on cotton fiber. The pH change measured is a response to growth on the noncellulosic constituents of the fiber and must be supplemented by further tests if one is to determine whether or not structural damage to the fiber has occurred.

Damage resulting from microorganisms occurring in increasing amounts of apparently good spinnable Middling cotton and the effects on mill processing are recognized. Such cottons, called "cavitomic," are distinguished from off-color and field-damaged types. Data and obser vations supporting a previous publication, together with methods of observation, are given. Reducing-material content, pH, and metallic-ion content of easily soluble water extracts are dis cussed, and relationships between them shown. Weakening of the fiber is exhibited by shorten ing of staple. Data obtained under both laboratory-controlled and conventional warehouse- storage conditions are given.

The results of the study of a forest floor of Arenito Bauru Soil are summarized as follows: The organic matter content of A00 and A0 horizons was determined by the loss on ignition method. The determination of the total carbon by the dry combustion method and subsequent calculation of the organic matter by the factor 1.724 was tound to be inadequate, judging from the low results obtaneid. Organic matter content of the forset floor of Arenito Bauru Soil is from 50 to 100% of that found in the first 30 cm of the soil mass, indicating a rapid decomposition of the same in the soil profile. Although Waksman (15) showed that lignin is the organic compound most resistent to the attack by the soil microorganisms, it was found that working with a soil from a different climatic region, lignin decomposes as quickly as all the other soil organic fractions. Therefore, concerning the fraction anti on of organic matter and the resistence of the compounds thus obtained to the decomposition by microorganisms, the idea was advanced of an approximately equal rate of decomposition for all the fraction for this soil type with the exception of the nitrogen compounds and water extract compounds. The fractionation of organic nitrogen compounds indicates enrichment of protein content in the soil with depth. It was determined that the losses of non nitrogen constituents were higher than those of nitrogen compounds. The accumulation of the latter in the soil takes place in the form of protein and related compounds. The C/N. ratio falls from 20 - 30 in the L layer to 10 - 14 in the layer a rising in b and e layers, which shows a definite washing of non nitrogen organic compounds into these horizons. | No estudo da serapilheira nos solos de mata do Arenito Bauru foram feitas as seguintes observações: Elaborou-se uma nomenclatura específica, dada a carência de termos técnicos em português, para denominar as diferentes camadas que constituem os horizontes orgânicos das matas. A matéria orgânica nos horizontes A00 e A0 foi determinada pelo processo de perda ao rubro e não pela multiplicação do teor de carbono por 1,724, porque, na serapilheira, este último processo conduz a resultados menos exatos. Apesar de não coincidirem exatamente as coletas de serapilheira com a dos perfis do levantamento pedológico já efetuado anteriormente no local, a sua associação permitiu esboçar o estado da matéria orgânica nestes solos. A quantidade de matéria orgânica da serapilheira oscila entre 1/2 a 1 da quantidade contida nos primeiros 30 cm do solo (camada a). O emprêgo do fogo para eliminar os restos vegetais das matas recém-derrubadas ou dos restos de cultura, é prática condenável em qualquer tipo de solo, mas, neste, assume aspecto ainda mais grave. Pelo estudo do fracionamento da matéria orgânica das diferentes camadas, constatou-se decomposição muito intensa, mesmo para a lignina, que é a base das substâncias humificadas. Como o levantamento pedológico já havia indicado, estes solos são pobres em substâncias orgânicas, mesmo no início da sua exploração agrícola. O estudo do fracionamento das substâncias nitrogenadas indica um enriquecimento do nitrogênio protéico, quando comparado com a matéria orgânica total. Deve haver perdas de nitrogênio, porém, muito menores que as das substâncias não nitrogenadas. A concentração, das frações nitrogenadas, à medida da evolução da matéria orgânica, é muito grande, caindo a relação C/N de, aproximadamente, 21-30 na camada L a 10-14 na camada a.