STRUCTURE AND GROWTH n 



say that we usually understand by it a sizeable, 

 self-supporting, woody plant with a single stem. 

 Trees have a definite place in the vegetable world. 

 They are plants which, in order to get light and 

 moisture, lift their leaves higher in the air than the 

 average, and push their roots deeper and wider 

 in the soil. This is the ruling principle which has 

 controlled the development of trees, and which has 

 made them as successful as they have been in their 

 struggle against their plant competitors. It has 

 controlled almost completely their shape, struc- 

 ture, and manner of growth. So great is the 

 height to which they must attain in order to over- 

 top their herbaceous and shrubby rivals for light, 

 that so much growth cannot be produced in a single 

 season. The growth must be cumulative, lasting 

 over from one season to another, and must be 

 strong and elastic, so that it will support large 

 leaf-surfaces high up in the air. The tree must 

 spread out, too, as well as go up, for in that way 

 it can get the greatest amount of light and can 

 save for its own use the nutriment and moisture 

 in the soil below it, by preventing evaporation and 

 the growth of other plants. As it grows higher 

 and wider every year, gaining a greater and greater 

 advantage over its competitors, its framework 

 must become proportionately stronger and 

 stronger. In other words, its trunk and branches 

 must grow. The roots must spread farther and 



