Plant Migration Studies 3 



of all kinds, whether or not they show any special adaptations 

 for wind carriage. 



A second general agent in dissemination is moving water, upon 

 which seeds and fruits may float from place to place. Every 

 brook, every creek, every river carries thousands of seeds, many 

 of which ultimately float to the banks, or are lodged upon sand- 

 bars and islands. In the aggregate the number of seeds carried 

 in this manner is large, but the number of trees resulting from 

 their growth is by no means as great, since many seeds are in- 

 jured by prolonged soaking in water, and in addition many do 

 not find favorable conditions for growth when cast ashore. 



Animals of various kinds are active agents in the dissemination 

 of seeds and fruits, especially of trees. Here the means of trans- 

 portation are much more efficient, since they may result in the 

 dispersal of seeds in all directions, and often for much greater 

 distances. Squirrels, rats, mice, and other rodents which carry 

 and secrete stores of food, and many herbivorous mammals which 

 feed more or less commonly upon seeds and fruits, are efficient 

 means for distributing the seeds of trees and other plants. To 

 these must be added the birds of nearly all species, excepting 

 those that subsist wholly upon animal food. Their power of 

 swift flight enables them to transport seeds long distances in 

 every direction, across barriers which are practically impassable 

 for quadrupeds. The number of different species which take 

 part in seed dissemination is not less than two hundred in the 

 portion of the central plains included within the boundaries of 

 Nebraska, and of these probably one-third carry the seeds of 

 trees. 



Nebraska occupies a central position in the United States, and 

 is somewhat south of the centre of the North American conti- 

 nent. It lies between latitude 40° to 43° north of the equator, 

 and longitude 95°3o' to 104° west of Greenwich. It lies almost 

 wholly in the Great Plains region, or the "Prairie Province" as 

 denominated by Pound and Clements in the "Phytogeography of 

 Nebraska." In the valley of the Missouri River along its eastern 

 •border its elevation above sea-level is 268 metres (880 feet) at 

 the southeast, and about 335 metres (iioo feet) at the northeast, 



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