Hygroscopy

“ In a hot summer, when the deficiency of moisture prevents the absorption of alkalies, we observe the leaves of the lime-tree, and of other trees, covered with a thick liquid containing a large quantity of sugar; the carbon of the sugar must, without doubt, be obtained from the carbonic acid of the air. The generation of the sugar takes place in the leaves, and all the constituents of the leaves, including the alkalies and alkaline earths, must participate in effecting its formation. ”

“ If the development of the plant is arrested by want of a saccharine or nitrogenous substance, and the liquid dries up, the 385 protoplasm contained in the cell contracts, and the spores, or endogenous reproductive organs, of the plant will remain in a state of rest, become perfectly dry, and yet retain life. They are not easily killed, even when subjected to a very high or low temperature, they do not lose the power of germination when favourable conditions present themselves, and at once take on a new birth. ”

“ Probably no subject in the whole domain of cryptogamic botany has wider bearings on agricultural science than the study of the flora and changes on and in manure and soil. Nitrifying bacteria play a very important part by providing plant life with a most necessary food. They occur in the soil, and two kinds have been described—the one kind converting ammonia into nitrous acid, and the other changing nitrous into nitric acid. We are principally indebted to Winogradsky for our knowledge of these bacteria ”

“ When the yeast-cells have only limited nutriment, with an abundant supply [178] of air, at a suitable temperature, an endogenous formation of spores takes place. The protoplasm of the cells divides into 1–4 (rarely a greater number) masses (Fig. 182 c, d, e) which surround themselves with a thick cell-wall, and in this state can withstand adverse conditions and periods of dryness lasting for several months.
The sporangia are not asci since they have no definite form, and a definite number, form and size of spores is not found. ”

“ As a matter of course, the several organic compounds contained in plants may continue to exist in soils for some time, varying according to conditions of temperature and moisture. Thus dextrin, glucose, and even lecithin and nuclein have been reported to be found. The activity of the numerous fungous and bacterial ferments under favoring conditions will, of course, limit the continued existence of such compounds somewhat narrowly, so that they can hardly be considered as active soil ingredients save in so far as they favor the development of the bacterial flora. ”

“ If we take two parts of white sugar and rub it up in a mortar with one part of a perfectly dry solid, the German yeast before spoken of, it is immediately transformed as if by magic into a flowing liquid mass—a syrup. This process of forming “invert sugar” can be watched under the microscope; the liberation of carbonic acid gas in large bubbles is seen to go on simultaneously with the assimilation of the dextrose, and the breaking up of the crystals of sugar; the cell at the same time increasing in size as well as in refractive power ”

“ This heat, indispensable to the phenomena which observation detects, is furnished by the decomposition of sugar. The position is the same as in the case of the decomposition of sugar in the presence of yeast-cells living without air. This decomposition of the sugar is manifested in the fruit by the production of alcohol and of carbonic acid. Here the ferment is the cell of the parenchyma of the fruit. There is in this cell a life kept up, or a chemical process accomplished, without air; according to our theory, fermentation should be present there, and experiment shows that it is. ”

“ Some micro-organisms grow best in a slightly acid, others in a slightly alkaline, medium. For example, for the growth and characteristic appearances of the comma bacillus of Asiatic cholera a faintly alkaline soil is absolutely essential. This slightly alkaline medium will be found to answer best for most micro-organisms, and may be obtained as follows:—With a clean glass rod dipped in the mixture, the reaction upon litmus-paper may be obtained, and a concentrated solution of carbonate of soda must be added drop by drop until red litmus-paper becomes faintly blue. ”

“ Clinging to every tree, stone, or animal tissue is a small quantity of moisture varying with the temperature, the amount of water in the air, and with other well-known factors. It is impossible to rid any natural substance wholly of water without heating it to a high temperature. This water which, apparently, belongs to all natural objects is commonly called hygroscopic water. Hilgard states that the soils of the arid regions contain, under a temperature of 15 deg C. and an atmosphere saturated with water, approximately 5-1/2 per cent of hygroscopic water. ”

“ The body of the spore containing most of the chlorophyll elongates more slowly, and divides by a series of transverse walls so as to form a short row of cells, resembling in structure some of the simpler algæ (C) .
In order to follow the development further, spores must be sown upon earth, as they do not develop normally in water beyond this stage.
In studying plants grown on earth, they should be carefully removed and washed in a drop of water so as to remove, as far as possible, any adherent particles, and then may be mounted in water for microscopic examination. ”

“ Summary.—The significance of hygroscopic moisture in connection with plant growth may then be thus summarized:
1. Soils of high hygroscopic power can withdraw from moist air enough [Pg 201] moisture to be of material help in sustaining the life of vegetation in rainless summers, or in time of drought. It cannot, however, maintain normal growth, save in the case of some desert plants.
2. High moisture-absorption prevents the rapid and undue heating of the surface soil to the danger point, and thus often saves crops that are lost in soils of low hygroscopic power. ”

“ Experiments made by Professor Dewar and Sir W. Thisleton Dyer, and reported to the British Association, upon the effect of the temperature of liquid hydrogen upon the germinative power of seeds, go to show that life goes on at a temperature so low that ordinary chemical action is practically stopped. Seeds of barley, vegetable marrow, mustard, and the pea were immersed in liquid hydrogen for six hours, cooled to a temperature of 453° F. below the temperature of melting ice, and came out unchanged to the eye, and, when planted, all germinated. ”

“ One cubic centimeter of diluted suspension is placed in a petri dish and mixed with a suitable nutrient agar medium, melted, and cooled to about 40° C. The medium sets, and after a few days’ incubation the organisms multiply and produce colonies visible to the naked eye. By counting these colonies we obtain an estimate of the number of bacteria in the one cubic centimeter of suspension, it being assumed that every organism has developed into one colony, and by multiplying this number by the degree of dilution we obtain the numbers per gram of soil. ”

“ The plant gets its phosphorus from phosphoric acid, its potassium from potash, and its calcium from lime.
There is a class of plants which have the power of taking free nitrogen from the air. These are the leguminous plants; such as clover, beans, cowpeas, alfalfa, soy bean, etc. They do it through the acid of microscopic organisms called bacteria which live in nodules or tubercles on the roots of these plants (Figs. 34-35) . Collect roots of these plants and find the nodules on them. The bacteria take nitrogen from the air which penetrates the soil and give it over to the plants. ”

“ HYGROMETER (Gr. ὁγρός, moist, μέτρον, a measure) , an instrument for measuring the absolute or relative amount of moisture in the atmosphere; an instrument which only qualitatively determines changes in the humidity is termed a “hygroscope.” The earlier instruments generally depended for their action on the contraction or extension of substances when exposed to varying degrees of moisture; catgut, hair, twisted cords and wooden laths, all of which contract with an increase in the humidity and vice versa, being the most favoured materials. ”

“ The favourable temperature is 37° C., and it will only grow very slowly at or below room temperature.
An excellent culture is generally obtainable in glucose gelatine. The growth occurs, of course, only in the depth of the medium, and appears as fine threads passing horizontally outwards from the track of the needle. At the top and bottom of the growth these fibrils are shorter than at the middle or somewhat below the middle. For extraction of the soluble products of the bacillus glucose broth may be used. ”

“ But, aside from temperature reactions and space requirements, there is no law which has yet been discovered which determines the character of the energy-storage compound which any given species of plant will elaborate. The process of photosynthesis would seem to be identical in all cases, at least up to the point of the production of the first hexose sugar; but the transformation of glucose into other monosaccharides, disaccharides, and polysaccharides seems to be a matter which obeys no rule or law. ”

“ Spore-formation has not been observed, but the protoplasm may be broken up, producing appearances which may be mistaken for spores. Actively motile, provided, some with a single and others with very numerous flagella, which are from three to five times as long as the bacillus itself. They stain readily in aqueous solutions of aniline dyes; and grow rapidly at a temperature 371 of about 60° Fahr. In plate cultivations minute colonies are visible in thirty-six to forty-eight hours; they are circular or oval, with an irregular margin. ”

“ In monœcious and diœcious algals the female conceptacles are distinguished from the male by their olive colour. The spores, when developed, are borne on a pedicle emanating from the inner wall of the conceptacle. They rupture the outer wall at its apex; at first the spore appears simple, but soon after a series of changes takes place, consisting in a splitting up of the endochrome into six or eight masses of spheroidal bodies. A budding-out occurs in a few hours’ time, and ultimately elongates into a cylindrical thread. ”

“ In size and form they are, within certain limits, exceedingly variable, although form and size are tolerably constant in the same species. At first all are globose; as they mature, the majority are ovoid or elliptic; some are fusiform, with regularly attenuated extremities. In Hygrophorus they are rather irregular, reniform, or compressed in the middle. Sometimes the external surface is rough with more or less projecting warts. Some mycologists are of opinion that the covering of the spore is double, consisting of an exospore and an endospore, the latter being very fine and delicate. ”

“ And not only so, but the yeast must be alive in order to exert these peculiar properties. If it be crushed, if it be heated so far that its life is destroyed, that peculiar power of fermentation is not excited. Thus we have come to this conclusion, as the result of our inquiry, that the fermentation of sugar, the splitting of the sugar into alcohol and carbonic acid, glycerine, and succinic acid, is the result of nothing but the vital activity of this little fungus, the torula. ”

“ The formation of a massive body naturally involves the localization of the absorptive region, and the function of absorption (which in the simpler forms is carried out by the whole of the vegetative part of the mycelium penetrating a solid or immersed in a liquid substratum) is subserved by the outgrowth of the hyphae of the surface-layer of that region into rhizoids, which, like those of the Algae living on soil, resemble the root-hairs of the higher plants. ”

“ A protuberance then grows out from one side of the sphere, and, rapidly increasing in length, assumes the character of a hypha. The latter penetrates into the substance of the potato-plant, either by entering a stomate or by boring through the wall of an epidermic cell, and ramifies, as a mycelium, in the substance of the plant, destroying the tissues with which it comes in contact. As these processes of multiplication take place very rapidly, millions of spores are soon set free from a single infested plant; and from their minuteness they are readily transported by the gentlest breeze. ”

“ The method adopted is to make as fine a suspension as possible of a known quantity of soil sample in a known amount of water, dilute this to 1⁄5000, 1⁄10000, and so forth by regular gradations, incubate cubic centimetres of the final dilution on artificial media in petri dishes, and count the colonies of fungi developing in each plate. Using the average figures from a series of duplicate plates, the number of “individual” fungi in a gram of the original soil sample may then be calculated. ”

“ The phenomenon of fermentation is still for him one which accompanies the decomposition of the constituents of the cell, rather than their building up by vegetative growth. "When the fungus ceases to grow, the bond which holds together the constituents of the cell contents is relaxed, and it is the motion which is thus set up in them which is the means by which the yeast cells are enabled to bring about a displacement or decomposition of the elements of sugar or other organic molecules." ”