April, 1908.] The Vegetation of Cedar Point. 
3 J 5 
Secondary Species: 
Opuntia humifusa, 
Oenothera biennis, 
Asclepias syriaca, 
Oenothera oakesiana, 
Andropogon furcatus, 
Panicum scribner ianum, 
Arabis canadensis , 
Apocynum cannabinum, 
Ceratodon purpureus, 
Cladonia sp. 
Cyperns schweinitzii, 
Euphorbia polygonifolia, 
Acerates viridiflora, 
Asclepias tuberosa, 
Species belonging more properly to other adjoining forma¬ 
tions are as follows: 
Quercus imbricaria, 
Rhus aromatic a, 
Arctostaphylos uva-ursi 
Strophostyles helvola. 
Quercus velutina 
Ptelea trifoliata, 
Toxicodendron pubescens, 
Polanisia graveolens, 
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 slight 
breeze was so faint as to be inappreciable, the temperature of the 
air at a height of U 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 
