ECOLOGY OF NORTHERN MICHIGAN. 35 



the under growth of which consists principally of Dwarf Cornel, Creeping 

 Snowberry, Labrador Tea, Pitcher Plant and Gold Thread on a thick carpet 

 of 'Sphagnum and other mosses. 



The fauna of these bogs is not characteristic. The mammals are repre- 

 sented by Hoy's Shrew, Southeastern Red Squirrel and Red-backed Mouse, 

 and the molluscs by Zonitoides arborea, Zonitoides exigua, Pyramidula 

 striatella catskillensis, Pyramidula asteriscus, Helicodiscus lineatus, Strobilops 

 virgo, Punctum pygmaeum, Vitrea ferrea, Sphyradium edentulum, and Pallifera 

 hemphilli. all forms that are abundant in the deciduous forest. 



That certain forms, for example the Pitcher Plant and Sphagnum, that 

 characterize the southern tamarack swamps are also restricted to the same 

 habitat in this region, and the fact that the climax flood-plain society is 

 evidently of the deciduous forest type, suggests that the cassandra and 

 coniferous societies will be ultimately replaced in the flood-plain succession. 

 But, on the other hand, the wide distribution in this region of many of the 

 forms that are largely confined to bogs further south, such as the Balsam Fir, 

 Dwarf Cornel and Red-backed Mouse, Starnosed Mole, and Southern Varying 

 Hare, indicate that the conditions w r hich permit the boreal forms to hold 

 certain swamps to the south are here more wide spread; while the similarity 

 between the bog and flood-plain societies indicates, as might be expected, 

 that the more nearly related habitats are the most noticeably and probably 

 the first to be modified by the change of conditions. 



Station IV. Substation 1. The amphibious forms of the mud flats grade 

 into the aquatic forms of the river by such marginal forms as Dulichium 

 arundinaceum and Sagittaria. The slow current of the river is an important 

 factor in determining the nature of this habitat, as it results in conditions 

 similar to those that prevail in ponds, thus permitting a biota adapted to 

 pond conditions to gain a foothold. The vegetation, although poorly rep- 

 resented, is decidedly of the quiet water type, being composed principally 

 of the Yellow Pond Lily, and Myriophyllum, and to a small extent of the 

 Sweet Scented White Water Lily, and Potamogeton natans, Fig. 19. 



The fauna also shows the effect of the slow current, but, owing to lack of 

 data on the habitats of the different forms, it is impossible to determine 

 definitely to what extent it is modified by the changing conditions. It is, 

 however, evident in a general way, for the forms that occur here are all forms 

 that occur in ponds as well as streams, while the characteristic river forms 

 that occur in the streams after they leave the mountains are apparently 

 not represented. For example, the molluscs found here, Amnicola limosa, 

 Ancylus parallelus, Valvata tricarinata, Physa sp. and Planorbis exacuous, 

 hirsutus and campanulatus, were all found on the vegetation and are forms 

 that, according to Baker, inhabit ponds and streams with aquatic vegetation 

 and mud bottom, but Limnaea decollata, that occurs on the bare rocky bottom 

 in the swift waters of the lower parts of the river, is apparently absent. 

 The fish are represented by the Fine Scaled Sucker, Horned Dace, Spawn 

 Eater, Trout Perch, Yellow Perch, and Nototropis cayuga. The Horned 

 Dace is, according to Forbes, almost entirely confined to brooks and small 

 streams. It is very abundant in Carp river, especially in the head waters, 

 and may thus be taken to represent the stream conditions that still prevail, 

 but in the quiet waters near the lake, there are associated with it the deeper, 

 quiet water, bottom feeders, the Yellow Perch and Sucker, while the charac- 

 ., teristic stream forms such^s the Brook Trout and Grayling were not found. 

 Certain other forms are so closely associated with this habitat that they 

 must be listed here; the more conspicuous of these are the dragon flies, 



