91 



causes a rapid scattering of certain plants along valleys and 

 over plains and brings prominently into view the effect of 

 barriers and the consequent distribution due to topography. 

 But even loftv mountains are not always efficient barriers 

 r.gainst the wii'id as the higher we go on a mountain the strong- 

 er is the wnnd. This is shown well by its curious effect on 

 trees growing on elevated ridges. Some naturally large trees 

 are flattened out in their growth so that they become creepers 

 instead. During the winter the fierce winds pack the snow 

 around the lower branches and preserves them while above 

 the top of the drift it drives the fine particles of ice so hard 

 against the exposed twigs that they are cut or cracked off and 

 so the tree does not extend upward but spreads over the 

 ground and at length forms an impenetrable mat wholly unlike 

 the nature of the tree. Illustrations of these are shown in the 

 two photographs appended. 



Another valuable factor and similar in effect to the wind is 

 the distribution by streams and rivers. The difference between 

 them being that the wind carries the lighter seeds and those 

 specially fitted for floating in the air in all directions as far 

 as the barriers, but the water transportation carries seeds of 

 any size and in only one direction. 



Since fleshy fruits cannot be distributed by wind and in 

 only one direction by water, there would be a dearth of these 

 most valuable plants were it not for birds, especially those 

 without gizzards. The birds are not greatly affected by bar- 

 riers unless they are very extensive or high, while the seeds 

 carried by birds are more liable to be dropped in suitable 

 places since the carriers are most likely to spend more time 

 in similar places to those in which they found the fruit. Other 

 animals, especially those with fur, are ready means of carrying 

 fruit and its seeds, and particularly other seeds covered with 

 gum, resin, barbs, or hooks, but such distribution is greatly 

 affected by barriers. All the above methods of distribution are 

 the principal ones as to rapidity. The slower methods are 

 those by stolons, offshoots, runners, etc., and ''" 



local. 



Barriers are of various kinds, the most important ar 

 areas of a similar flora such as a great and moist plain wl 

 a prairie or forest, hot or cold, a great desert, or lofty ] 

 tains covered with different floras. It matters not how 

 seeds are transported for if they do not fall where the cli 



