1910] Bruncken, Studies in Plant Distribution. 151 



vegetation is entirely absent, not only in the lower, but also the 

 middle zone. The shingle beach, being very narrow, hardly shows 

 zonal differences. But the sandy middle beach is the special abid- 

 ing place of Cakile. < )f course it is very far from covering it, — 

 its plants stand singly, many feet apart ; but it is practically the 

 only species found in this zone. In great contrast to this is the 

 upper beach, where a fairly considerable number of species may 

 be found. The number of both species and individuals increases 

 in proportion to the amount of material that has been washed 

 down from the clay bank. Generally speaking, the nearer the 

 foot of the bank, the more luxuriant the vegetation. 



Among the species most abundant on the upper beach are : 

 Cakile edentula, Lathyrus maritimus, Blymus canadensis, Poten- 

 tilla anscrina. Euphorbia polygonifolia, Bquisetum arvense, Physa- 

 iis pubeseens, Salix lougifolia, Salix nigra, Popidus deltoides, 

 Rhus typliina. The willows, cottonwood and sumach are invaria- 

 bly plants but a few years old, which would indicate that their 

 success is precarious. In a few places such weeds as Salsola tra- 

 gus, and Xant liium eanadense, which are now absent from few 

 vacant places on the uplands, have established themselves. 



Of these species, Cakile, Euphorbia and Potentilla are found 

 exclusively on the beach 3 , Lathyrus occasionally invades the bank ; 

 all the rest are far more generally distributed on the bank, and may 

 therefore be safely considered as invaders from above. 



The upper beach is very far from being completely clothed 

 with vegetation. At most on a few alluvial fans this condition is 

 approximated. The following were the number of plant individ- 

 uals found in 1902 on a stretch of sandy upper beach near White- 

 fish Bay, two hundred feet long and twenty wide, which may be 

 considered as fairly typical : Cakile edentula, 25 individuals ; 

 Bquisetum arvense, 10; Physalis pubeseens, 3; Populus deltoides, 

 two years old. 3 ; same, one year old, 1 ; Rhus typhina, two years 

 old, 1. Other species, of course, will come in elsewhere, but the 

 number of individuals will, I think, be fairly constant, and so will 

 the proportion of Cakile and Bquisetum. 



At Milwaukee, the upper beach is remarkable for being quite 

 different from the floristic aspect of similar stations both north and 



5) Euphorbia polygonifolia is common in a few places only. Near 

 Ryan in the town of Oak Creek, it grows abundantly in an upland pasture, 

 near the shore, on clay soil. 



