Exposure of roots is also sometimes effected by winds displacing sandy soils liable to shifting in dry weather, and the resulting wilting of the plants thus exposed at their roots may be supplemented by damage due to the repeated impact of the wind-driven sharp grains of sand, which act like a sand-blast and erode the tissues.
In many of the cases given above the principal result is the weakening or destruction of the chlorophyll action. This means a loss of carbohydrates—sugars, starches, etc.—and in so far a starvation of the plant. The injurious effects are quantitative and cumulative: if large areas of foliage are concerned, or if the effect lasts a long time, the plant suffers from loss of food, and may die. In those cases where the effect is due to the cutting off of supplies at the roots, and where the yellowing is a secondary symptom, the disease is more general in character, and recovery is often impossible, because the loss of water cannot be compensated, and the results may be further complicated by the gradual penetration of poisonous matter into the cells. It is frequently necessary, though sometimes very difficult, to decide which is the primary and which secondary (or tertiary, etc.) symptoms in the order of their importance, and the diagnosis may be complicated by a number of accessory factors which it is impossible to treat generally.
Notes to Chapter XIX.
The principal cases here described are dealt with in works on plant physiology, and in the works of Sorauer and Frank already referred to.
As regards damage due to uprooting of seedlings by frost, see Fisher, "Forest Protection" (Engl. ed. of Hess' Forstchutz), in Schlich's Manual of Forestry, Vol. IV., 1895, pp. 439-442.
On Albinism, see Church, "A Chemical Study of Vegetable Albinism," Journ. Chem. Soc., 1879, 1880, 1886.
Beijerinck's results are contained in his paper, "Ueber ein Contagium vivum fluidum," etc. (with English abstract), in Verhandl. d. Kon. Akad. v. Wetensch, te Amsterdam, 1898. Koning's paper is in Zeitschr. f. Pflanzenkrank., Vol. IX., 1899, p. 65. See also Nature, Oct. 11, 1900, p. 576.
