70 Lloyd and Tracy : The insular Flora 



the lobes of the leaf on their chief veins, and Canavaiia by bring- 

 ing the leaflets separately into the vertical by means of the motile 

 organs at their bases. 



Strophostyles Juivola, on the other hand, is a plant of wide 

 northern distribution. It is of much smaller stature, but has very 

 much the same ecological development as Canavaiia. No one of 

 these plants may be described as dominant in this region, except 

 in one restricted locality on Breton Island where the two species 

 of Ipomoca form a network covering the soil much as described by 

 Schimper. (See Plate 8.) They do not, however, even here 

 serve to attract other plants and the association is poor in species. 

 Associated with the just mentioned prostrate forms are a few 

 sedges and some grasses, notably Spar Una and Panicum amarum, 

 the latter in isolated clumps between which usually germinate the 

 seeds of the prostrate vines already named and from which the 

 plants extend their runners in various directions, but chiefly toward 

 the lower beach. 



The upper beach extends from the upper limit of high water 

 and ordinary wave action, and shades off on the inner side into a 

 sand plain formation to be considered beyond. The name upper 

 beach is less appropriate than back strand, because the zone, 

 properly speaking, is not a beach, as Cowles has pointed out. 

 The term strand has, however, been given a much wider applica- 

 tion, so we choose for our present purposes the word beach. The 

 upper beach, then, is composed of very low dunes, caused by ac- 

 cumulations of sand about the grass, Panicum amarum, which here 

 attains full development. Associated with Panicum amarum, a 

 maritime plant found as far north as Long Island, is another large 

 grass of more southern distribution, Uniola paniculata, which 

 grows in scattered clumps, adding to the otherwise monotonous 

 grass of the beach dune vegetation a very striking element of 

 beauty in its gracefully curved large inflorescences. Uniola 

 paniculata is, however, of much less importance as a sand-bind- 

 ing grass than it appears to be on the east coast of Florida or on 

 Ocracoke, according to Webber (u) and Kearney (6), respec- 

 tively. The quantitative relation, stated by Webber, namely, that 

 in Florida it forms 75 per cent, of the vegetation is about reversed. 

 Panicum amarum taking the lead to that extent. 



