22 FARM FORESTRY 



leaves it is carried down through the soft or inner bark and 

 into the tree through the pith rays. The sap never passes 

 downward through the wood of the tree. 



How Trees Reproduce Themselves. Trees reproduce them- 

 selves principally by seeds and by sprouts. A few trees pro- 

 duce seed every year but most trees produce heavy seed crops 

 only every two or more years. Seed production requires a 

 large amount of food. This the tree stores up and after a 

 seed year most trees require some time to lay up sufficient food 

 to produce another crop. Trees in the open produce seed more 

 often and in greater abundance than trees in the woodlot owing 

 to the larger crowns. In the woodlot trees produce seed only 

 on the upper portions of the crown which are exposed to the 

 light. Usually a large part of the seed produced by trees is 

 infertile. 



Most trees are very particular in regard to the character 

 of the seed bed or the ground on which the seed germinates. 

 Some trees like hemlock and yellow birch like a moist seed bed. 

 These trees are often found starting on rotting stumps or logs 

 or on moss. The seed of many other trees requires the mineral 

 soil for germination. Some, like the pitch pine, cedar and 

 gray birch will grow on dry soil in full sunlight. Others de- 

 mand shade for germination. Where the ground is too hard 

 and dry for the tender roots from the seed to penetrate, no 

 seedlings will be produced. 



Trees vary in the arrangements for scattering the seed 

 and the distance to which the seed is sown. Light seeded trees 

 like ash, tulip, cottonwood and willo\v will scatter their seed 

 long distances in the wind, often a mile or more in heavy winds. 

 Many seeds have wings or other contrivances which cause the 

 seeds to whirl about as they fall or which hold them in the air 

 so that they are blown far from the seed trees. Trees with 

 heavy seed like oak, hickory and chestnut can sow their seed 

 only under their crowns, except as the falling seeds strike 

 branches and bound away from the tree or roll down a slope. 



