392 THE POPULAR SCIENCE MONTHLY. 



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 pro- 

 vides means for the healing of injuries produced in this way, and in 

 many cases it is possible for very extensive injuries to be healed with- 

 out any aid beyond Nature's own efforts. Grape-vines and other 

 vigorously growing plants often exhibit a most remarkable recupera- 

 tive 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 re- 

 moving 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 exter- 

 nally 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 heal- 

 ing was complete in the interior of the stem, but the line of section 

 was plainly visible under the microscope. 4. The union of the epider- 

 mis and tissues immediately below was not accomplished, and there 

 was thus left, by shrinkage of the parts, a groove which extended com- 

 pletely 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 



* "Phenomena of Plant Life," Clark. 



