356 BOTANICAL GAZETTE [NOVEMBER 



we find the greatest variety of tree species, among which are Fagus 

 atropurpureus, Quercus rubra, Ulmus americana, Platanus occidentalis, 

 Acer saccharum, Tilia americana, Acer saccharinum, Fraxinus 

 americana, Gleditsia triacanthos, Liriodendron tulipijera, Gymnocladus 

 dioica, Cercis canadensis, Asimina triloba, and Celtis occidentalis. 



The clay morainic area is dominated by Quercus rubra, Q. alba, 

 Q. velutina, Hicoria ovata, H. glabra, Acer rubrum, Ulmus americana, 

 and Quercus macrocarpa. 



In the region of the interlobate moraine the disappearance of 

 the more mesophytic forms is quite marked. The forest is there 

 largely composed of Quercus coccinea, Q. macrocarpa, Q. velutina, 

 Q. alba; and as we go northeastward these become associated with 

 Pinus strobus. Quercus prinoides forms a characteristic shrubby 

 growth along the roadsides and in waste places. 



Such is the forest background in which are set the thousands of 

 acres of bog and swamp, and to which the groves of Larix laricina 

 exhibit a marked contrast. These tamarack areas are to be seen 

 on all sides in the region of the interlobate moraine; they are quite 

 common in the clay morainic belt, but are practically wanting on the 

 lake plain. 



As one follows along the morainic country from northern Indiana 

 into the " thumb "of Michigan, he passes from a region dominated 

 by a rich mesophytic broad-leaved forest to one of conifer and xero- 

 phytic broad-leaved ascendency; from a region whose low grounds 

 are characterized by a swamp flora to one in whose depressions the 

 bog flora reaches a high state of development. In this connection 

 it is interesting to note that one finds this gradual change epitomized 

 in the Huron valley as he goes from its mouth to its source. 



METEOROLOGICAL CONDITIONS. 



Under this head we shall consider the general meteorological 

 conditions of the Huron basin, and compare them with the meteor- 

 ological conditions found about the center of the distribution of bog 

 plants (55, p. 406). In general, this center extends from Lake 

 Winnipeg through the upper Great Lake region down the valley of 

 the St. Lawrence to the Atlantic coast. It is in the coast provinces, 

 however, that the bogs reach their highest development, in the form 



