324 Annals of the; Carnegie Museum. 



plains/® the seedling fails to find there the necessary moisture and 

 never succeeds. 



In the Pinus Strobus formation the shrub, herbaceous, and ground - 

 layers consist of scattering individuals of the following species : 



Smilax herbacea, Vaccinium corynhbostim, 



Cypripediiim acaiile, Lycopodium clavatiim, 



Pyrola americana, Lycopodium complanatum, 



Pyrola elliptic a, Lycopodium lucidulum, 



Pyrola secunda, Lycopodium obscurum, 



Chimaphila maculata, Unifolium canadense, 



Chimaphila umbellata, Vagnera stellata, 

 Morchella esculent a. 



The reaction of the Pinus Strobus formation upon its habitat is 

 probably relatively greater than that of the heath, but it consumes 

 a much longer period of time. The heath, as indicated by the rela- 

 tive sizes of the junipers, ordinarily occupies its habitat not more than 

 thirty years before being replaced by the Pinus Strobus formation, while 

 the latter occupies its habitat for approximately two hundred years. 

 The soil in the pine forest is everywhere covered with a layer of pine 

 needles and in the older portions of the forest, beneath the upper 

 layer of undecayed needles, is a layer of more or less completely 

 humified organic material often more than one inch in thickness. 

 The line of demarcation between the lower part of this layer, which 

 represents the sandy loam of the heath, is not so distinct as in the 

 heath, owing probably to the decay of roots and fungal mycelia, and 

 perhaps indirectly to some extent to the percolation of hydrostatic 

 water. The action of earthworms, so important in many soils, is not 

 indicated in this soil. 



The accumulation of a mulch of forest litter, a thick layer of humus, 

 and the gradual distribution of humus throughout the sand beneath, 

 are processes tending directly or indirectly to increased capillarity, 

 humification, nitrification, the formation of various acids, and the 

 further decomposition of the grains of sand with the production of salts 

 available in solution in the water of the soil as plant-food. The soil, as 

 left by the Pinus Strobus formation, as compared with the soil as left 

 by the Arctostaphylos-Juniperus heath has a more uniform supply of 

 available (capillary) moisture and also a greater supply of mineral 



^9 Britten, W. E. /. c, pp. 578 and 579. 



