400 Annals of the Carnegie Museum. 



fluence transpiration. Transeau found that in a general way, " The 

 southeastern area where the rainfall is from loo-iio per cent, of the 

 evaporation, corresponds to the region of the Deciduous Forest center," 

 and that in the Southern Appalachians at least, the region with the 

 ratio above no per cent, coincides with the southern extension of the 

 Northeastern Conifer Forest, while the forest center in the St. Lawrence 

 basin is marked by ratios above loo per cent. 



The ratio for the city of Erie is not less than no percent., but 

 the instruments of the U. S. Weather Bureau Station there are about 

 1 80 feet above Lake Erie and it is probable that the ratio for Presque 

 Isle, but a few feet above the lake and within reach of its more imme- 

 diate effects upon humidity, temperature, etc., would be found to be 

 considerably higher. However the ratio would vary greatly between 

 the various habitats on the peninsula itself; as, for instance, between 

 the interior of the sand-plain, with its loose sand fully exposed 

 to wind and insolation, and the interior of the black oak forest, 

 with its shaded, humus-covered soil, the temperature of which never 

 presents the rapid and extreme variations of the surface of the sand- 

 plain. The rainfall-evaporation ratio would probably be below 100 

 for the sand-plain and perhaps a careful instrumental determination 

 of the factors would show that there is a constantly increasing ratio 

 from the sand-plain to the black oak forest, which could be correlated 

 with the shifting of the relationship of the respective formations from 

 the northeastern conifer forest to the deciduous forest. 



The lower and drift beaches of Presque Isle are under the equaliz- 

 ing influences of the water to such an extent that they are inhabited 

 by a formation found in similar habitats almost throughout North 

 Temperate America, but removed from the more immediately modi- 

 fying influences of the water, the sand-plain, with its sterile, porous, 

 wind-exposed soil, supports a formation including several distinctly 

 northern species : Artemisia canadensis, Laiiiyrus maritinius, or, 

 around the lagoons and ponds in the sand-plain, Triglochin palustris, 

 Carex aqiiatilis, C. gronovii, C. oederi puntila and C. canescens, 

 Jiincus balticus, J. artictclatus, Salix syrticola, Hypericum boreale, etc., 

 or, on the dunes in the sand-plain, Primus pumila. 



With the advent of considerable numbers of woody species upon the 

 sand-plain its southern portion is occupied by the Myrica thicket, 

 which must be regarded as having southern affinities, while the north- 

 ern portion of the sand-plain is occupied by the Arctoslaphylos-Juni- 



