Page:The Olive Its Culture in Theory and Practice.djvu/152

124 HONEY DEW. The Honey dew consists of a gummy sugary perspiration on the leaves, especially on the under side, on the flowers, and on the young branches. This substance sometimes forms itself into a varnish uniform in its deposit, and at others into drops like dew. This disease attacks the Olive, Poplar, Linden, Orange, Walnut, Willow and Elm trees and also the grape vine. The real cause of it is unknown. Some writers think that the viscous matter is exuded from the cochineal insect which infests the plants, but others have observed that this disturbance exists both on trees in the open air, and on those enclosed in greenhouses where there were no insects. The popular idea is that the humor emitted by the morbid leaves is a production of the plant itself, caused by the unfavorable influence of a hot, dry soil. Admitting this to be the probable cause, the remedy would be copious fertilizing and to prune the tree so as to keep the top in proportion to the spread of the roots.

SCAB. The scab manifests itself in wart-like excrescences as large as walnuts, often affecting the youngest and most slender branches. The plant impoverished by this pest takes on a languid appearance and sometimes dies. Ordinarily this evil is met with on soil that is low or too rich and not sufficiently ventilated, or where trees are placed too near together, in trees excessively pruned, or in those maltreated in the gathering of the fruit by beating with poles. Some writers hold the opinion that the scab is caused by either a vegetable or animal parasite, but the most diligent microscopic observations have never revealed the presence of an insect, either before, after, or contemporaneously with, the apparition of the small protuberances. The cause therefore must arise from some disturbance of the functions provoked principally by contusions, either from hail storms or by poles in beating down the fruit, by excessive pruning, or by absence of light and air. The contusions of the cortical