THE DECIDUOUS FOREST CLIMAX. 195 



Jennings (1908, 1909) has studied the water sere of the coasts of Lake Erie 

 at Cedar Point in Ohio and Presque Isle in Pennsylvania: 



He recognizes two successions: (1) lagoon-marsh-thicket-forest, and (2) bay- 

 marsh-thicket-forest. The former comprises the following communities: 

 Potamogeton formation, Nymphaea formation, Castalia-Nymphaea formation, 

 Juncus-Heleocharis formation, Sdrpits-Typha formation, Sabhodia-IAnum iat- 

 mation, Cladium-Calamagrostis formation, Decodon-Persicaria formation, 

 Cephalanthus-Cornus formation, Myrica-Salix formation, Rhus-Alnus format 

 tion, Populus-Sdlix formation, Prunus-Acer formation, Alnus-Acer formation. 



These are variously combined in different areas, giving many sequences, of 

 which the following are illustrations: (1) Potamogetonr-Nymphaea, Scirpus- 

 Typha, Cladium-Cakmiagrostis, Myrica-Salix, Populus-Salix; (2) Potamogeton, 

 CastaliOfNymphaea, Decodon-Persicaria, Cephalanthus-Cornus, Rhus-Alnus, 

 Ulmus-Acer. The bay-marsh-thicket-forest development is essentially the 

 same, as is shown ia the cove habitat with the following sequence: Chara, 

 Potamogeton, Castalia-Nymphaea, Phragmites-Typha, Rhus-Alnus, Ulmvs-Acer. 



Transeau (1908) has measured the evaporation by means of the porous cup 

 in the lowest stratimi of a series of habitats on Long Island. The stations and 

 the rates of evaporation in per cents are as follows: 



(1) garden, standard, 100 per cent; (2) garden, high level, 80 per cent; 

 (3) gravel slide, open, 100 per cent; gravel shde, partly invaded, 60 per cent; 



(6) forest, open, 50 per cent; (6) forest, typical mesophytic, 33 per cent; 



(7) forest, raArine type, 13 per cent; (8) forest, swamp type, 10 per cent; (9) (10) 

 upper beach, 83 per cent; (11) salt marsh, outer margin, 123 per cent; (12) salt 

 marsh, inner margin, 83 per cent; (13) fresh-water marsh, 50 per cent. 



The author notes that the evaporation ia the course of reforestation decreases 

 from 100 per cent in the open gravel slide to 33 per cent in the lowest stratum 

 of the climax forest, and that the ecesis of Trillium, Arisaema, and Veratrum 

 was successful in the swamp forest with 10 per cent, finally unsuccessful in the 

 open hillside forest at 50 per cent and absolutely prohibited in the gravel shde 

 at 100 per cent. The reaction of pioneer vegetation is also shown by the fact 

 that the evaporation in the partly invaded gravel slide was 60 per cent in con- 

 trast with 100 per cent in the open gravel slide. The fact that the xerophytic 

 upper beach showed less evaporation than the garden indicates clearly that 

 evaporation must be considered with reference to water content, especially at 

 the critical period. 



Burns (1909 : 445) has summed up a comparative study of the bogs of the 

 Huron River Valley in the following conclusions : 



"The chief factor determining the position of the greatest amount of peat 

 deposit and the width of the zones of plants at the local peat bogs is the depth 

 of the water in the different parts of the original postglacial lakes. The chief 

 factor in determining the position of the open water is depth; given time 

 enough, the open water will disappear from all our lakes. In places where the 

 water is very shallow, the bog flora is imable to get a start because of the wave- 

 action caused by the winds and on account of the shoreward push of the ice. 

 Such places, however, bear no definite relation to the points of the compass! 

 Different zones of plants follow in a definite orderly succession: lily, bog-sedge 

 bog-shrub, tamarack, maple-poplar." ' 



Harshberger (1909 : 53) has studied the conversion of lakes into bogs on the 

 Pocono plateau of Pennsylvania. The serai relation of the zones of the lakes 

 is indicated by the following sequence about Half Moon Pond: 



