114 



sand and comes in only in the deepest part of the blowout. Polytri- 

 chum, on the other hand, may colonize in relatively dry sand., where 

 it at once produces moist conditions by its dense growth. 



Still farther in the rear and also somewhat higher is a deposit 

 of sand representing a later stage in the refilling of the basin. It has 

 been stabilized by Panicitm v'lrgatwn and Lespedeza capitata. 

 Besides these, Solidago ncmoralis, Hudsonia tomentosa, and Panknui 

 pseudopnbcsccns indicate a reversion to bunch-grass. Over this 

 whole area mats of Polytrichum are appearing. Some mats are large, 

 confluent, and dense ; others small, regularly circular, and with very 

 small plants near the margin. These are coming in everywhere, 

 even under the bunches of Paiiicuni virgatiim and Paniciiui psciidopu- 

 bescens, or surrounding Hudsonia tomentosa or Solidago ncmoralis. 

 Coming up with it are many plants of Solidago graminifolia, Aris- 

 tida tuberculosa, Rhcxia virginica, Polygala sanguinea, and in the 

 deepest parts a few plants of Scirpus cyperinus. On the larger and 

 older mats these species are small or absent, and other species more 

 characteristic of the association occur. These are Salix pedicellaris, 

 J^'iola lanccolata, and Spiranthcs ccrnua. A few depauperate plants 

 of Panicnni pscudopubcsccns persist even in the dense mats of the 

 moss. Along the south and west margins of this area almost pure 

 mats of PolytricJiuui extend to the very edge of the blowsand (PI. 

 XII, Fig', i; XII, Fig. 2), reaching a height of three feet (9 dm.) 

 above the Salix association already described. They are associated 

 only with the three typical species just mentioned. Throughout this 

 area Solidago graminifolia and Aristida tuberculosa occur, but they are 

 most abundant on the bare sand between the mats. As the Polytri- 

 chum increases and finally occupies all the surface, these will be 

 forced into a marginal zone, as in blowouts B and C. 



THE SWAMP ASSOCIATION. 



In tlie Dixon area, just south of blowout D, is a long- north and 

 south excavation (PI. XIII, Fig. i), with rather steep walls of bare 

 sand on either side. These walls represent a partially stabilized wind- 

 ward slope, and are occupied by Carex umbcUata, Aristida tuberculosa^ 

 Panicnni pscudopubcsccns, and Solidago ncuioralis. In the deepest 

 parts are two ponds, B and F, surrounded l)y definite zones of vege- 

 tation. The bottom of the ponds is a black muck w^ell mixed with 

 sand. The water-level fluctuates with the weather. When visited 

 in August it was one foot (3 dm.) above the basin of blowout D, 

 6.4 feet (2.1 m.) above the country to the east, and 16 feet (5.4 m.) 



