188 MASS. EXPERIMENT STATION BULLETIN 170. 



practiced. All fertilizers should be applied evenly. Spreading by hand 

 is at best a poor method, as shown by the dark green plots of grass on 

 lawns where nitrate of soda has been applied in this way; but when 

 fertilizer spreaders cannot be had the hand method must be used. Another 

 factor to be considered when applying fertilizers to lawn trees is that the 

 grass roots will obtain their full share. Turning under the sod and cul- 

 tivation of the soil around the tree is of 

 the greatest importance from the very 

 considerable amounts of organic matter 

 added to the soil. Fertilizers applied 

 under these conditions, or, far better, 

 stable manure well incorporated into the 

 soil at the rate of 20 to 30 cords per acre, 

 are of the greatest benefit to the tree, 

 even if it becomes necessary to reseed 

 immediately. In cases where it is incon- 

 venient or undesirable to disturb the 

 soil around a tree, and when the applica- 

 tion of fertilizer to the surface does not 

 accomplish the desired results, holes 1 or 

 2 feet apart and 15 inches deep may be 

 made with an iron bar and then filled at 

 different times with a liquid fertilizer. 



There are a number of fertilizer mix- 

 tures prepared for shade trees that are 

 undoubtedl}^ of value, but some of them 

 are apparently not based on any expert 

 knowledge of the tree's special require- 

 ments. 



Fig. 61.— Re-enforced wire clotli 

 tree guard, sliowing edge stiffen- 

 ing with nail holes for attaching 

 to tree. (From the Wright Wire 

 Company.) 



Diseases of Trees. 



Trees, like other living organisms, are 



very liable to attacks from disease, and a 



tree of any maturity is seldom found 



perfect in all respects. A disease may be defined as a disorder caused by 



any failure in or diversion of the normal physiological activities of the 



organism. 



The diseases of plants with M-hich plant ])athologists have to deal may 

 be divided into three classes: First, those caused by parasitic fungi; 

 examples, — rust, smut, etc. Second, those brought about by functional 

 irregularities which induce saprophytes (dead wood fungi) or parasites 

 to thrive, such as "damping off," mildew, etc. Third, those of a purely 

 functional nature, laathogenic organisms not necessarily being present; 

 examples, — dropsy or oedema of tomatoes, malnutrition and others. 

 All these types of diseases are found in trees, but the first and second are 

 most common. 



