April, 1908.] The Vegetation of Cedar Point. 315 



Secondary Species: 



Opuntia humifusa, Oenothera oakesiana, 



Oenothera biennis, Andropogon furcatus, 



Asclepias syriaca, Panicum scrihnerianum, 



Cyperus schiveinitzii, Arabis canadensis, 



Euphorbia polygonifolia, Apocynum cannabinum, 



Acer ate s viridiflora, Ceratodon purpureus, 



Asclepias tuberosa, Cladonia sp. 



Species belonging more properly to other adjoining forma- 

 tions are as follows: 



Quercus velutina, Quercus imbricaria, 



Ptelea trifoliata, Rhus aromatica, 



Toxicodendron pubescens, Arctostaphylos uva-ursi, 



Polanisia graveolens, Strophostyles helvola. 



The willow appears in places to dominate the formation dur- 

 ing a good part of the growing period and under such conditions 

 may de designated the Salix interior Society. Over limited areas 

 of the older and more protected parts of the Sand Plain the 

 Arenaria serpyllifolia Society and the Arabis lyrata Society 

 characterize quite conspicuous vernal aspects. 



The minor structure of this formation requires much further 

 study. Especially after a careful instrumental determination of 

 the environmental characteristics of the various parts of the 

 habitat, a considerable modification might be found necessary. 

 Among the more prominent characters displayed among compo- 

 nent species of the formation may be mentioned the relatively 

 large proportion of biennials and perennials. The formation 

 during the hot portion of the summer is subjected to extremely 

 severe and xerophytic conditions, at least during short periods, 

 and it is probably to this that the structure af the vegetational 

 formation is due. ■ The formation is essentially an open structure 

 and often displays prominent ecological families and communities 

 as, for instance, with Opuntia humifusa, Asclepias tuberosa, etc. 



Certain instrumental observations were made in parts of the 

 sand plain during the summer of 1905 as to temperature, relative 

 humidity, etc., and, as showing the extremely xerophytic condi- 

 tions to which the plants of the sand plain are exposed at times, 

 the following records may be of interest. On a day in middle 

 August, 1905, in one of the open spaces between the advance 

 guard of the oak forest north of the Laboratory where the sHght 

 breeze was so faint as to be inappreciable, the temperature of the 

 air at a height of 1^ feet was 83 degrees Fahrenheit, while the 

 sand at the surface just beside one of the communities of Opuntia 

 humifusa was 142 degrees, taken at 1 :30 p. m., while the maximum 

 temperature for the day reported by the U. S. Weather Bureau 



