i 9 o6] TRANSEAUBOGS OF THE HURON RIVER VALLEY 39 



dry sand. Palisade tissue was developed in the leaves of these plants 

 in diffuse light, and it is shown that palisade tissue is to be correlated 

 with physiological drought. An analogy between the bog habitat 

 and the dry sand habitat is established. 



Experiments with Larix indicate that mycorhizas develop only in 

 poorly aerated substrata; their growth is exceedingly slow; the 

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

 naturally or artificially aerated substratum favors the development 

 of normal roots, and these roots when not surrounded by water 

 develop root hairs abundantly. Larix seedlings can withstand 

 prolonged submergence. When exposed to low substratum tem- 

 peratures and poorly aerated soil conditions, Larix produces more 

 xerophilous leaves. 



Further field work on the bog plant societies needs to be carried 

 on in the region extending from Winnipeg to New Brunswick. Data 

 on the soil and air temperatures, the acidity, the chemical composition 

 of the soil solution, and the plants associated in bog areas throughout 

 this region will go far toward solving the problems of the distribution 

 of bog plants. Experimentation on the production of xerophilous 

 structures by bog conditions should be continued on a larger scale 

 than is possible in the ordinary university plant-house. 



To Professor V. M. SPALDING and Professor F. C. NEWCOMBE, 

 of the University of Michigan, under whose direction this work was 

 planned and carried out, I desire to express my sincere thanks both 

 for helpful suggestions and the facilities of the institution which were 

 freely placed at my disposal. Many thanks are also due Professor 

 I. C. RUSSELL for criticism of the physiographic part of this paper. 

 I wish to acknowledge the kindness of Mr. FRANK LEVERETT, of 

 the U. S. Geological Survey, whose intimate knowledge of the glacial 

 geology of this region has been most helpful to me in the prosecution 

 of my own field work. To Mrs. N. L. BRITTON I am indebted for 

 the determination of the mosses. Finally I take this opportunity 

 to express my appreciation of my friend and former instructor, Dr. 

 H. C. COWLES, to w r hose writings and lectures I owe my interest 

 in ecological botany. 



UNIVERSITY OF MICHIGAN. 



