456 BOTANICAL GAZETTE [December 



later ones being superimposed upon earlier layers; that they were 

 formed in the course of a characteristic sequence or succession of 

 vegetation units; and that the layers are more or less evidently 

 connected with responses to changes in basic habitat factors. 



It is of great importance to realize the influence which structural 

 differences in the peat deposits exert upon the progress of peat-land 

 agriculture, upon the advancements in the peat fertilizer industry, 

 and upon improvements in mechanical devices for excavating, 

 pulping, drying, or converting peat into fuel and other products. 



Peat investigations in this country have reached the stage where 

 basic correlations are possible between pleistocene geology, the dis- 

 tribution of peat deposits and their post-glacial vegetation units, 

 and the climatic factors which in the past controlled the develop- 

 ment and structure of peat accumulations. Clements 3 has recog- 

 nized the need of extending peat investigations into the past, 

 correlating geology, climatology, and the migration of former plant 

 populations. A complete study of peat deposits is no longer possible 

 without the aid of other sciences. It will now be practicable to 

 extend European investigations dealing with climatic changes to 

 the morainic systems of North America and to show whether or not 

 glaciations have been contemporaneous, whether they depended 

 upon general or local causes, and whether plant populations have 

 immigrated and were affected by alternating dry and humid periods. 



The information upon the different types of peat material offered 

 in Bulletin 802 will aid in a tentative way, it is hoped, toward a 

 solution of various peat-land problems. There are numerous ques- 

 tions in physical, chemical, and bacteriological studies, and also in 

 physiological investigations dealing with peat materials which can 

 now be attacked more successfully from this new standpoint. 



The improvement of the present situation in matters of drainage, 

 the management and the general uses of peat deposits for agri- 

 culture and for technical industries, should become obvious if con- 

 sideration is given to the structural differences of deposits, especially 

 to those deposits where systematic field experiments are to be 

 carried out or various lines of practices are to be tested. Peat- 



3 Clements, F. E., Plant succession: An analysis of the development of vegetation, 

 pp. 512. Carnegie Inst. Washington, publ. 242. 1916. 



