HARSHBERGER: AMERICAN HEATHS AND PINE HEATHS 179 



below the lead sand and meadow ore, and a humus sandstone is formed. 

 This is called Ortstein and forms an impervious layer. The roots of 

 pine trees are unable to penetrate this layer and flatten out on it. 

 The pine trees become stunted, their branches gnarled and the tree 

 finally dies to be replaced by others which pass through the same cycle 

 unless the tap-root manages to pass through a hole into the subsoil. 

 The phytogeographic investigations of the writer have shown that 

 on the island of Nantucket we have true heaths, called moors by the 



Fig. 2. Bear oak {Quercus nana) in heathland, Nantucket. September 7, 



I9M- 



inhabitants. Typic heather plants grow on the sandy and gravelly 

 glacial soils of the island and there is a formation of dry peat on the 

 surface of the soil. The low, rolling hills are covered with plants in 

 different groupings, so that in places the western prairies are suggested, 

 while in other places the Roman Campagna, especially where the 

 vegetation has been browsed by cattle. The plain-like character of 

 the vegetation is suggested in those areas where the beard grass 

 {Andropogon scoparins) covers the ground in exclusive growth, except 

 where patches of heath plants are found such as the huckleberry 

 {Gayhis'sacia resinosa) and the bearberry {Arctoslaphylos uva-iirsi) 

 (Figs. 3 and 4) which forms mats, or carpets of large extent. Another 

 common plant, which suggests the Scotch heather {Calluna vulgaris), 



