248 NATiHAi. kk(;knej{atiun ov woods. 



own weight down a slope. ^Vllen air cunents are the carrying' 

 agency it is necessary that tlie seed should be sufficiently liglit, 

 and that when it falls the wind should blow from the right 

 direction. In this respect the species, the force of the air 

 current, and the relative position of the regeneration area and 

 the mother trees are of importance. The seed of some species, 

 as poplar, is so light that it travels for miles, while that of 

 others falls straight to the ground. Gayer gives the following 

 distances for a number of species under the influence of a 

 moderate air current. 



Birch, elm, larch, 4 — 8 times the height of the trees. 



Spruce, Scotch pine, 



alder .... 3 — 4 ,, ,, ,, 



Maple, ash, horn- 

 beam .... 2 — 3 ,, ,, ,, 



Lime, silver fir . . 1 — 2 ,, ,, ,, 



Beech and oak, scarcely beyond the reach of the crowns. 



In the case of strong winds the distances are proportionately 

 greater ; instances can be seen in Scotland where Scotch pine 

 seed has been carried to many times the distances given above. 

 The distances are also greater, if the mother trees stand at a 

 higher elevation than the regeneration area. 



The direction of the wind during the fall of the seed intro- 

 duces a great element of uncertainty, as it can only in rare 

 cases be relied on. 



A further complication may arise if the seed sliould fall 

 during the prevalence of a dry east wind, while, for other 

 reasons, regeneration should commence in the east and 

 gradually proceed towards the west. 



Ik Siiihihle Coiiililinn of the (Hfrminaliini llrd. 



This has often to be provided by working, or woimdiiig the 

 soil. Where the roots of the trees are grubbed out the soil is 

 sutiHciently stirred, but where the stools remain in the grou)ul 

 wo)kiiig may be necessary. 



