200 A NATURALIST IN THE GREAT LAKES REGION 



kidney-shaped. The young leaves as well as the branches are 

 downy. 



Leatherleaf shows well the characteristics of this group of 

 xerophytes. Its leaves are thick and glossy with the wax in 

 the epidermis; the under side of the leaf is scurfy — all devices 

 to prevent the loss of w^ater. One wonders at such xerophytic 

 characters in shrubs growing in a swamp. But while water is 

 abundant it seems to be difficult for the root hairs to absorb 

 it. This is explained, in part at least, by the low soil tempera- 

 ture and the acidity of the soil. These conditions also prevent 

 the decomposition of the plant debris accumulating from season 

 to season, since they check the activity of the soil bacteria so 

 necessary for this process. This debris accumulates, therefore, 

 as peat instead of decomposing to help form humus as it would 

 in most soils. 



Next to the cassandra zone comes the tamarack zone 

 (Fig. 226) with tamarack or larch trees as the most conspicuous 

 plants. These are deciduous conifers with the needles in clusters 

 of sixteen or more. Where these trees stand thickly, few plants 

 grow under them, except the sphagnum which usually covers the 

 ground. The soil is wet, peaty, and cold, for the sunHght does 

 not penetrate the dense tamaracks readily. Soil temperature 

 remains about 35° F. even in midsummer. In the more open 

 parts of the tamarack bog, in addition to the herbaceous plants 

 of the cassandra zone which invade it to some extent, there are 

 found the rush aster (Fig. 243), swamp rose, Rosa virginiana 

 with its stout hooked prickles, red-osier dogwood, poison sumac, 

 (Fig. 107) and several ferns, the crested shield-fern (Fig. 244), 

 royal (Fig. 203), and cinnamon ferns (Fig. 205). 



Shoreward from the tamarack zone there occurs a transition 

 zone that varies according to the environment. One may pass 

 from a t^'pical black oak dune association to the tamarack bog 

 society in a dozen steps, or the bog may gradually change to an 

 interdunal swale of one of the preceding types. The transition 

 may be from an oak-hickory forest in moraine country through 



