Commelina zirginica Crotonopsis lincans 



Rumex AcctoscUa Oenothera rhoiiibipetala 



Polygonum feiiue Monarda punctata 



Mollugo vcrtkiUata Hedeoma hispida 



Silene antirrhina Linaria canadensis 



Talinuni rugospennuni Brigeron ramosus 



Lepidium virginicum Ambrosia psilostachya 

 Arabis lyrata 



Comparing the lists of perennials and interstitials, it will be noted 

 that the latter group is represented by more species, while the number 

 of individuals is vastly greater. The perennials are also infrecjuent 

 in comparison with the more general distribution of the interstitials. 

 The species in twelve quadrats of approximately four square meters 

 each, in the Hanover area, were listed. The results are shown in 

 the following list, where the numeral indicates the number of quad- 

 rats in which the species occurred : 



Ambrosia psilosiachya (12) Linaria canadensis (10) 



Lepidium rirgijiicum (9) Helianthus scaberrimus (4) 



Lithospenmiui Gmclini (2) Acerates viridiflora, var. 

 Oenothera rlionibipetala (i) lanceolata (2) 



Croton glandulosus, var. Solidago nenioralis (i) 



septentrionalis (i) Silene antirrhina (i) 

 Polygala polygama (i) 



The relative frequency of the perennials and interstitials in the 

 list is as 35 to 100. This may be compared with the data given in 

 the description of the bunch-grass association, where in tw'o cases 

 the relative frequencies were as 56 to 100 and as 172 to 100. The 

 interstitial vegetation varies somewhat from place to place, and any 

 species may be locally very abundant. In general, the three leading 

 species in the list are the most important of the group. At any sta- 

 tion the species are generally closely similar to those found in the 

 neighboring- bunch-grass. 



The greatest number of individuals of perennials is found in 

 young associations which have but recently displaced the original 

 bunch-grass, and the number decreases continually with age. The 

 individuals of interstitial species increase in numl)er as the available 

 space becomes larger, but when so much surface is exposed that the 

 blowing of the sand becomes too rapid or continues too long in spring 

 and early summer, the number begins to decrease. 



None of the species with conspicuous flowers is abundant enough 



