.' 



ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 177 



cucuUafa^ Geranium maculatumj Oxcdis strida and Phlox 

 divaricata occur. Later some of these disappear and give 

 place to Geum alhum^ Poientilla canadensis^ Heuchera ameri- 

 cana^ Oxalis cymosa^ Engeron annuuSj Polemoriium replanSj 

 Cynoglossum virginicum, Hedeoma pulegioideSj Scutellaria 

 canescens and S. versicolor. In the fall Galium Aparine, G, 

 concinmimy Eupatorium ageratoides, and Vernonia novebora- 

 censis take their places, as do Monarda fistulosa and Pycnan- 

 themum linifoliumj the rosettes of which have been in evidence 

 during the greater part of the year. Where the thicket is 

 more or less open, one finds, during the spring months, Del- 

 phinium tricornej Thalictrum purpurascens, Podophyllum pel- 

 latum, Cypripedium puhescens^ Arisaema Dracontiumj and A. 

 triphyllum. 



THE MISSOURI BLUFF. 



The cHff. 



This, on the Missouri side, is limited to the upper portion 

 of the bluff, the walls of which are almost perpendicular and 

 sometimes even concave. Here and there ledges occur on 

 which soil accumulates as it does in the numerous crevices of 

 the limestone. Occasionally larger blocks of the latter have 

 become separated frorn the main body, and, being thus more 

 exposed to the action of the elements, show the full extent of 

 the disintegration caused partly by the weather, partly by 

 the dissolving influence of the water and partly by plant 

 action (plate 12, 2). The shallowness of the soil and the ex- 



posed position, resulting in an almost total loss of the water 



brin 



com 



forming annuals, and a fall flora of rosette-forming biennials 

 and perennials. The principal vernal plants are Arahis. 

 canadensis^ Capsella Bursa-pastoris, Draba cuneifoliaj Erysi- 

 mum asperum, Lechea major, Silene antirrhina, Astragalus 

 mexicanus, Polygala verticillata, Heuchera hispida, Andro- 

 sace occidentalis , Phlox pilosa, Lithospermum canescens, 

 Monarda Bradhuriana and Scutellaria parvula. The princi- 

 pal spring grasses are Melica diffusa and Panicum depau- 

 peratum. Numerous perennials enlarge their rosettes at this 



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