142 MASSACHUSETTS HORTICULTURAL SOCIETY. 



as coiiveuieut places for fasteuiug horses. lu short, that a tree 

 should be so treated that it may develop a symmetrical form and 

 luxuriant foliage is nobody's business, while, on the other hand, it 

 is assumed that it is the right of every one to fasten his horse to- 

 any tree he pleases or to use the branches as supports for wires. 

 The march of improvement, as it is called, never respects the 

 trees. If a sidewalk is to be widened, down go the trees, or their 

 roots are chopped off in such a way as to injure them. If some 

 enterprising man wishes to build a new house on the site of an old 

 one, the old house is sold for a song and is moved off to some 

 distant part of the town, being dragged along through narrow 

 streets crushing and maiming the trees on the way, just as if these 

 public ornaments were of no account compared with private gain. 

 In fact, it sometimes seems as if a good many people believed 

 that one could not do anything to a tree which really would injure 

 it, and that a tree is so constituted that it can grow on in spite of 

 all obstacles. 



We should begin by recognizing that a tree is a living thing 

 which is not only readily affected by the soil and atmosphere, but 

 is also sensitive to mechanical injuries to a degree which might not 

 at first be suspected. An animal tells us by its actions when it 

 has been injured. We know the injuries done to trees only by the 

 after effects, which may not be evident for mouths or even a few 

 years, and it is my special purpose today to call 3'our attention to 

 some of the injurious effects which follow mechanical injuries. 

 The subject is rather complicated and implies some knowledge of 

 the microscopic structure of trunks and branches, but I sliall 

 endeavor to avoid technicalities as far as possible. 



Before we can understand the harm done by mechanical injuries 

 we must first consider briefly the normal structure of the trunk. 

 If we examine with a microscope a cross-section of a very young 

 twig, we find that the surface is composed of a single layer of 

 thin, colorless cells called the epidermis, beneath which are several 

 layers of larger cells, many of which contain green coloring 

 matter. Then come the vascular bundles arranged in a ring, 

 although they are not really in contact with one another but are 

 separated by what we may call the rays, which pass from the pith 

 to the outer green cells, and are composed of cells not unlike 

 the latter in shape, that is, spherical or polyhedral, or some 

 simple modification of these forms. A longitudinal section 



