Plant Migratioji Studies 7 



and Key a Paha counties) it is highly probable that it occurs 

 somewhat sparingly and perhaps intermittently along the eastern 

 and northeastern border. 



Red Elm (Uliinis fulva Michx.) is abundant in the Missouri 

 River forest area, from which it has spread westward up the 

 river valleys nearly or quite half way across the state (19). 

 Beyond this area a single station is reported in Frontier County. 



The Ashes (Fra.viiiits spp.). Each cylindrical seed pod is pro- 

 longed upward into a flat oar-shaped, slightly bent and twisted 

 wing. Where the fruit separates from its pedicel it drops with 

 the heavier seed-end down, and is given a whirling motion by 

 the wing, and when caught by the wind is carried many metres 

 before it reaches the ground. 



White Ash (Fra.vinus aincricana L.) is common in the Alis- 

 e-ouri forest area, from which it has extended up along the east- 

 ern border of the state (22) to Sarpy County. 



Green Ash {Fra.vinus lanccolata Bork.) is also common in the 

 Missouri forest area, from which it has spread westward and 

 northward along the river valleys, across the state (24) to the 

 western counties. 



Red Ash (Fra.vinus. pennsylvanica Marsh.) is found with the 

 preceding (23) and apparently has been disseminated with jt. 



Red Bud (Ccrcis canadensis L.). The bean-like pods are 

 very flat and thin, and are well adapted to be carried in the wind 

 a few metres. It is common in the Missouri forests and has 

 extended northAvestward into Nebraska (36) as far as Lancaster 

 and Douglas counties. 



The Maples {Acer spp.). The bicarpellary fruit develops two 

 thin membranous curved and slightly twisted wings, one on the 

 back of each carpel. At maturity the carpels split apart, and 

 each falls slowly with a whirling motion, while the wind carries 

 it to a greater or less distance from the parent tree. In a high 

 wind this distance may be twenty to thirty metres, or even more. 



Mountain Maple (Acer glabrttni Torrey) is abundant in the 

 Rocky Mountains of Wyoming and southward, from which it 

 lias extended eastward into the extreme western part of the state 

 (42) at two stations (Sioux and Scott's BluflF counties). 



17 



