108 J- E. CRIBBS 



Sphagnum or Mnium, but may contain herbaceous species which 

 persist from the preceding deciduous stage, especially such as 

 can develop in poorly lighted situations. It should be noted 

 that the large majority of the species represented in the conifer- 

 ous swamp zone, which are not evergreen, are vernal forms. 

 These develop in greatest abundance along the inner edge where 

 it borders the deciduous stage, and along the outer portion where 

 it grades into the deciduous mesophytic forest of the moraines. 

 This disposition of the species is largely attributable to the fact 

 that they carry on a large part of their physiological work before 

 the deciduous trees mature their spring foliage. 



Pinus appears but sparingly in the hemlock stage, unless it 

 be upon slightly elevated ground. It, like the hemlock, has a 

 tendency to develop pure stands, and is found in better estab- 

 lished and drier situations. Both of these forms very conunonly 

 advance upon the uplands, where they become members of the 

 morainic forests. Such migrations are not very extensive, and 

 these species rarely become dominant members under such 

 circumstances unless special moisture conditions favor this 

 development. 



Upland Ponds 



Numerous small ponds are formed upon the moraines. They 

 commonly occur where clay lies at the bottom of depressions 

 and is in turn overlain by coarser glacial drift. The seepage of 

 water from the latter may be sufficient to supply the amount lost 

 by evaporation etc., or, as frequently happens, they may dry 

 up more or less completely during the latter part of summer. 



The vegetation associated with these has a different aspect 

 from that occuring in the great lowland swamps. There is a 

 notable absence of the sedge-bulrush stages, and a strong de- 

 velopment of the shrubby associations. Such ponds are com- 

 monly from ten to seventy-five yards in width, and since they are 

 usually surrounded by the morainic mesophytic forest, the humus 

 is built up quite rapidly by the decomposition of leaves and 

 fallen trees, which are added in excess to the humus formed 

 from the decay of plants within the area itself. 



