PREFACE. VI 1 



known facts, for which I am mainly indebted to general 

 treatises, monographs and shorter papers, 1 am constrained 

 to acknowledge for Part IV my special indebtedness to 

 NVarming' s Lehrbuch dcr okologischen Pflanzengeographie and 

 Ludwig's Lehrbuch der Pflanzenbiologie. 



C. R. B. 

 UNIVERSITY 01- CHICAGO, 



