34 BOTANICAL GAZETTE [JANUARY 



exceedingly slow, the fungus developing along with the root; (3) the 

 acidity of the substratum is not a factor in their development ; (4) in 

 a naturally well-aerated soil or in an artifically aerated substratum 

 normal roots develop; (5) when the roots are not surrounded by 

 water, root hairs develop abundantly. Mycorhiza therefore appears 

 to be an abnormal root condition. Whether the fungus is of advan- 

 tage to the root under these poorly aerated conditions cannot as yet 

 be stated. 



(8) In order to determine whether the zone of tamaracks follows 

 the shrub zone because of the occasional submergence of the sedge 

 zone, the following test was made: Ten Larix seedlings averaging 

 7 cm in height were placed in a crystallizing dish with the roots 

 imbedded in 2 cm of sphagnum. Over this a layer of bog water 4 cm 

 in depth was maintained for six weeks. The plants grew quite as 

 well as those in a peat substratum. Stem and root submergence is 

 therefore not a factor in preventing the growth of seedlings tamarack 

 in the sedge zone. The liability to submergence in the bogs I have 

 studied would not extend over nearly so long a period of time. 



V. Summary. 



The Huron River basin shows three well-marked physiographic 

 divisions which differ in forest covering and the possibilities for bog 

 development. These are (i) the region of the Saginaw-Erie inter- 

 lobate moraine; (2) the Erie morainic belt; and (3) the lake plain. 



In discussing the meteorological conditions of a region as affecting 

 the flora, attention is called to the fact that the significance of the 

 data is not apparent unless the temperature and rainfall phenomena 

 are compared with those of the, optimum region of dispersal of the 

 plant societies involved. In the case of the bog plant societies the 

 temperature of the region under discussion averages several degrees 

 higher during the summer months than the eastern maritime prov- 

 inces of Canada (the optimum region of dispersal for the bog plants), 

 while the rainfall during the same period averages about three- 

 fourths as much. This is believed to account for the general differ- 

 ence in character and development of bog societies in the two regions. 



Bog and lake basins are here associated with deposits of glacial 

 drift. The most frequent causes of these basins are (i) the melt- 



