Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 269 



association many miles from any woodland. The plant is seldom 

 seen upon exposed hilltops since it can not endure serious wind 

 action. The wild plum is also commonly seen in similar isolated 

 situations more or less completely surrounded by bunch-grasses. 

 Primus melanocarpa is likewise present in low bushy form in many 

 sites away from the streams. 



A species with a decided tree-form that occasionally develops 

 similar circumscribed patches in the "pockets" among the driest 

 hills is Celtis occidentalis. I have seen "hackberry pockets" with a 

 clump of about a hundred trees ranging in diameter from 1.5 to 8.0 

 inches and with a uniform height of 18 to 20 feet. Woodland birds 

 build their nests here far from the larger bodies of timber. The 

 most notable use of the "hackberry pockets" by birds is by the great 

 blue heron, Ardea herodias. These large birds take almost complete 

 possession of some of these groves and use them as nesting places 

 for many generations. 



The peculiar distribution of all of these species over the uplands 

 away from the woodlands is doubtless related .to the influence of 

 birds in seed carriage. 



Both xerophilous and mesophilous herbs are numerous within 

 the shade afforded by the trees of this association, as well as in 

 fewer numbers scattered through the various thickets briefly noted in 

 connection with the woodlands. The commonest of these are 

 included in the following alphabetical lists without regard to abun- 

 dance, frequency, or layerage. 



Herbaceous Species in or near Sandhill Woodlands 



SPECIES OF wide DISTRIBUTION 



Adicea pumila Galium aparine 



Agrimonia stricta Galium triUorum 



Apios apios Geum canadense 



Aster salicifolius Geum strictum 



Bromus ciliatus Homalocenchrus oryzoides 



Carduus altissimus Humulus lupulus 



Carex longirosfris Koellia virginiana^ 



Celastrus scandens Lappula americana 



Circaea lutetiana Macro calyx nyctelea^ 



Elymus canadensis Moehringia lateriflora 



Filix fragilis Monarda Ustulosa^ 



Fragaria americana Muhlenbergia mexicana 



