The best thing to do in such a case is to re pot the plant into fresh soil containing a little lime or wood ashes first washing off the old soil and trimming of the diseased roots. Good drainage must be furnished and over-watering avoided. It must be clearly understood that the roots of most plants require an abundant supply of oxygen, and that they will suffocate and die if they do not get it.
Poisonous materials in the soil are also often the cause of serious root injury. Illu minating has leaking from gas mains or pipes and diffusing through the soil in the minutest quantity kills and poisons the roots of all kinds of vegetation. The only thing to do in such cases is to stop the leak and air the soil.
The decomposition of organic matter, espe cially manures rich in nitrogen, in soils not well supplied with oxygen, results in the formation of products injurious to the roots of plants. In jurious acids are often set free from their com binations in the soil by the action of plant roots, bacteria and fungi and by chemical changes brought about by the use of certain fertilizers, like the acid of superphosphates. In all those cases a liberal addition of lime to the soil acts as a cure to the injured plant and corrects the acid condition.
Alkali In some cases, on the other hand, there is too much lime or other alkaline material such as carbonate of soda, etc., in the soil. The root hairs and feeding roots are killed by a sudden rise of a soluble alkali, or they may die a slow death if there is too much lime. It is a curious fact that a liberal addition of gypsum tends greatly to reduce the injury in both these cases and to raise the limit of endur ance of most crops of alkali. Where alkalis cannot be washed out of soils through proper drainage, much can be done by breeding and selecting varieties of plants better adapted to such conditions. Great progress has already been made in this direction with alfalfa, sugar beets, cereals, date palms, etc.
Soil Every green plant re quires for its healthy development, besides water, oxygen and the CO: of the air, a certain proportion of nitrogen in the form of nitrates or ammonia, a salt of potassium and of phos phoric acid, available calcium and magnesium in about equal proportion, sulphur and a trace of iron and chlorine. If these are not available to the plant in the right form or ratio, or if any of them is too greatly in excess or lacking, a diseased condition of the plants in such soils quickly develops.
Nifrogrn.—Lack of nitrogen in available form causes a proportionately diminished vegetative growth, light 'green or yellowish leaves, even where there is abundant moisture and other nutrient materials. An excess of nitrogenous fertilizer, on the other hand, causes various pathological derangements. Abnormal vegetative growth at the expense of flowers and fruit thus inducing temporary sterility is one of the commonest results of a food containing too much nitrogen in comparison with potassium and phosphoric acid. The tissues in such cases are likely to be soft and watery, easily injured by unfavorable temperature or moisture conditions as well as by insect and fungous parasites.
Tissue degeneration is in many cases the result of over feeding with nitrogenous fertilizer. This appears to be one of the commonest causes of " die back " or gummy degenera tion of the orange. Peaches and plums also' suffer from a similar malady from the same cause. Large gum pockets develop in the wood as a result of the degeneration of the cells. The movement of water and food materials in the plant is greatly interfered with. The wood does not mature properly and as a result winter kills, or it Is destroyed by insect and fungous parasites.
Phosphoric acid is an important constituent of every living cell, entering largely into the composition of the nucleus. Its reduction below the cell requirements is followed by a cessation of cell division and and in green Is disorganization of the firs place first in the maturer leaves, then in the younger parts. An application of phosphates or superphosphates usually promptly corrects these pathological conditions.
Potassium also is required in considerable quantity by all plants. One of the first signs in a plant of a lack of available potassium is a decided cessation of growth without other cause of trouble. During the early stages of potash starvation the plants often retain their normal green color. In later stages very little starch or sugar is made and almost no protein or nitrogenous matter. Unless the missing element is supplied the plants finally become yellow and slowly die. Potassium hastens and perfects the maturing of plants, especially the ripening of the wood of perennial plants, making them less liable to winter injury.