The North American Forest 29 



times left standing by settlers on their clearings 

 nearly always succumb to the wind sooner or later. 

 Some species, which have shallow roots under the 

 best conditions, are more liable to windfalls than 

 others. Such are, for instance, the basswood (Tilia, 

 Americana) and the hemlock (Tsuga canadensis). 

 Others, like the various walnuts and hickories, de- 

 velop deep and stout tap roots even in the most 

 sheltered situations, and consequently suffer little 

 from this particular danger. Windfalls are a great 

 detriment to the American forests. In addition to 

 the direct damage, the tangle of drying branches 

 and twigs affords one of the best starting-points for 

 the fires of which we will have much more to say 

 later on. The overturned trees are at once at- 

 tacked by a host of insects and fungi which some- 

 times spread upon the adjacent sound timber and 

 injure it. 



To return to the opportunities which tree seeds 

 find for sprouting, such as are small and perhaps 

 provided with wings, or other devices enabling them 

 to float for a while in the wind, have evidently a 

 better chance than heavy seeds which cannot fall 

 far from the parent stem. To the former class be- 

 long, among others, the seeds of poplars and 

 birches, while conspicuous in the latter are the oaks 

 and hickories. It is impossible to describe here 

 even a few of the wonderful devices by which 

 many seeds acquire this useful power to travel. 

 How much advantage a tree derives from such 

 power of its seeds can be seen conspicuously in the 



