240 State Horticultural Society. 



We believe under ordinary conditions the most satisfactory dis- 

 tance is twenty-six to twenty-seven feet each way. A planting much 

 in favor at this time is twenty feet apart north and south and thirty 

 feet east and west. The reasons given for this spacing are that it gives 

 the trees a better morning and evening sun, while each tree protects 

 by shading the body of the one just north of it during the heated 

 portion of the day. ■ Both these supposed facts are mistaken. On 

 June 21, when the sun has reached summer solstice, its northern de- 

 clination is twenty-three and one-half degrees, our latitude is thirty- 

 nine and one-half degrees, a difference of sixteen degrees. So that at 

 noon on that date the angle made by the oblique rays of the sun with 

 a perpendicular at our latitude is sixteen degrees, and the shawod cast 

 by a tree is sixteen-fortieths the height of the tree. A tree then 

 eighteen feet high would cast a shadow sixteen forty-fifths of eighteen 

 feet, or six and four-fifths feet. A tree then must be fifty-four feet high 

 for its noon shadow to reach the base of a tree twenty feet away. But 

 you f;iv, the heated season conies later, when noon shadow^s are 

 longer. Very well ; we will take another date. On August 5th (that's 

 hot enough) the sun's declination is eleven and one-half degrees north 

 and its rays strikcf us at an angle of tAventy-eight degrees on that date 

 at noon. A tree then casts a shadow tA\'enty-eight forty-fifths of its 

 height. A tree eighteen feet high would throw a shadow eleven and 

 one-fifth feet, but the tree to be protected is twenty feet away. So 

 fhere is not]iing in the noon shade theory. This is a problem of trigo- 

 nometry, but these figures are close, the error being against us. But 

 how about the morning and evening sun. You are aware there are but 

 two days in the year when the sun rises in the east and sets in the 

 west, namely March 21 and September 21, when the sun is at the vernal 

 and autumnal equinoxes, and we are not much interested where it 

 rises on these dates. From March 21 to September 21 it rises north 

 of east and sets north of west. The morning shade then falls to the 

 southwest and the evening to the southeast and trees get the sun what- 

 ever the spacing. At 8 :30, June 21, the sun is in the east and shadows 

 fall to the v.-est ; the sun's rays then strike us at an angle of forty-five 

 degrees and a tree will cast a shadow equal in length to the height of 

 ihe tree. A tree must be twenty-seven feet high for its shadow to reach 



