Page:Popular Science Monthly Volume 25.djvu/404

392 complete destruction of the plant or tree, together with the borers, by fire.

Where injuries are inflicted by man, proper attention in caring for the injured part will prevent the introduction of disease. Nature provides means for the healing of injuries produced in this way, and in many cases it is possible for very extensive injuries to be healed without any aid beyond Nature's own efforts. Grape-vines and other vigorously growing plants often exhibit a most remarkable recuperative power. One of the most notable instances of this kind was brought to my attention in 1874. During the early spring the bark of a weeping-willow was removed from the base of the trunk, making a complete girdle for a distance of eighteen inches from the ground. In some places the cambium tissue was not fully destroyed, and this materially aided in the healing process. From the upper part of the girdle, or, more properly, from the lower portion of the uninjured bark, a new growth was rapidly formed and pushed downward, soon taking the form of aerial roots. In one or two instances these became more or less connected with the trunk over the girdled portion, but most of them remained distinct, and all finally penetrated the soil, with which they established a normal connection. In another instance, when removing some young squashes from vines under experiment, the former were separated by a knife, but left in place for collection at a later time. One, however, was overlooked at the time of collection, and, when the final harvest was made, it was discovered firmly united to the stem from which it was originally separated, and had attained considerable size. Upon careful examination of the parts, both externally and under the microscope, it appeared that—1. When the cut was made the squash was not displaced, and the cut surfaces immediately came together again. 2. As determined by a "fault" in a crack of the epidermis, the squash rotated in position as the cut was made, thus accomplishing a displacement of nearly one quarter of an inch on the surface of a stem three quarters of an inch in diameter. 3. The healing was complete in the interior of the stem, but the line of section was plainly visible under the microscope. 4. The union of the epidermis and tissues immediately below was not accomplished, and there was thus left, by shrinkage of the parts, a groove which extended completely around the stem and demonstrated the completeness of the section in the first instance.

In these examples, therefore, we have illustrations of the inherent tendency of all plants to overcome disease and injury through the operation of vitality.

In soil influences we have to contend with conditions which are not always so easy to control, and, when once they have produced their effect upon the plant, the diseased condition is a somewhat difficult matter to correctly diagnose and treat. Soil influences operate in a