ECOLOGY OF NORTHERN MICHIGAN. 29 



]Jurr Oaks, associated with the Mountain Maple, Large-toothed Aspen, 

 Mountain Alder (Alnus alnohetula), several willows and scattered Red and 

 White Pine. The underbrush and soil cover of this zone is composed of 

 Polypodium vulgare, Juneberry, Scarlet Sumac, Bush Honeysuckle, Eastern 

 Ninebark, Great Bilberry, Round Leaved Dogwood, Dwarf Cornel, Narrow- 

 leaved Cow-wheat, Low Snowberry, Polypodium vidgare, and Lycopodium 

 clavatum, complanatum and selago; Linnaea americana may also be mentioned. 



Higher up the mountain the soil cover becomes replaced by the Bearberry, 

 Dwarf and Loav Black Blueberry, New Jersey Tea, and Creeping Winter- 

 green. The White Pines still persist, but the shrubs mostly disappear, 

 and the oaks and aspens associated with Juniperus nana become very 

 scrubby, often forming small mats on the shght soil. Fig. 12. 



As in case of the vegetation, the range of many of the animals of the 

 mesophytic forest reaches an upward limit in the aspen zone, where they 

 occur mingled with other forms that replace them on the bald areas. Thus 

 the molluscs become noticeably fewer in individuals in this zone; Zonitoides 

 exigua, Cochlicopa lubrica, Vitrea ferrea, Eucomdus fulvus, Helicodiscus 

 lineatus and Carychium exile seem to drop out of the fauna entirely, while 

 Punctum pygmaeum, Sphyradium edentulum, Zonitoides milium and arhorea, 

 and Strohilops virgo, by changing their habitats from the damp fallen leaves of 

 the mesophytic forest to the dry soil held by the heaths, are able to persist. 

 Mingled with these forms was found for the first time Bifidaria curvidens. 

 Similarly the only grasshopper that occurs in the mesophytic forest (Tettix) 

 is replaced in the aspen zone by Melanoplus luridus, jermoratus and islandicus, 

 Chloealtis abdominalis and conspersa, and Camnula pellucida, while the 

 "Northeastern Chipmunk, Northern Plains Skunk, Woodchuck, and the wood- 

 peckers, owls, chickadees, nuthatches, etc. are mostly replaced by the 

 Lake Superior Chipmunk, Junco, Robin, and Bluebird. The smaller 

 mammals such as the mice, moles and shrews seem to persist without notice- 

 able diminution in abundance. 



Station III. Substations 2, 5 and 6. On the mountain top beyond the 

 limit of the aspens and oaks, the biota is composed almost exclusively of 

 the forms that appear in the upper part of the aspen zone. The heaths, 

 represented by the Bearberry and Creeping Wintergreen, with the Dwarf 

 and Low Black Blueberry and New Jersey Tea, form a large dense mat 

 beyond the aspen zone, that extends in long tongues along the crevices on 

 the bare top. Fig. IL On the denser portions of this mat occur widely 

 scattered White and Red Pines with many dead stumps, Fig. 13. 



On the bare mountain top, the flora consists only of the lichens, Lecidea 

 lactea, Lecanora conspersa and cinera, Parmelia conspersa, and Stereocaidon 

 coralloides, on the surface of the rock, and a crevice vegetation of Harebell, 

 Three-toothed Cinquefoil, Wild Wormwood, Evening Primrose, Panicum 

 xanthophysum, Polypodium vulgare, Polystichium lonchitus, Asplenium 

 trichomanes, and Solidago bicolor, lanceolata, juncea and erecta. 



The molluscs, Punctum pygmaeum, Euconulus chersinus polygyratus, Zoni- 

 toides milium, Strobilops virgo, Vitrea indentata 'and Bifidaria curvidens, 

 that characterize the upper part of the aspen zone, also occur in the larger 

 heath mats, associated with Acanthinida harpa. Bifidaria curvidens greatly 

 predominates in this fauna. Dead specimens of Helicodiscus lineatus and 

 Succinea avara are often found in the rock crevices near the brink of the chff, 

 but these were probably blown here as they could hardly exist in this habitat, 

 being moisture loving forms. The characteristic insects of this station 

 are the dragonfly, Sympetrum obtrusum, the butterflies, Argynnis cybele, 



