HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 139 
L. and Hibiscus Moscheutos L. Outside of these associations and 
growing in the deeper water along the banks of the Delaware 
River is an association of Scirpus lacustris L. (Scirpus associa- 
tion) (Fic. 1, Q, near lighthouse). 
SWAMP-PLANT FORMATION. — The swamps of the region under 
consideration are of three kinds, as determined by their origin: 
(1) Swamps that owe their origin to a stream flowing over a low, 
ee oBo 
<0 OMOES % OP 
9 O95 
Crum ree 
Fic. 3. Portion of the tidal-marsh-plant formation shown in Fig. 1. A, dark green 
Zizania aquatica L. ; 
nN 
& 
(= 
oo 
aQ 
Ln) 
® 
o 
= 
i 
= 
Ss 
BS 
8 
S. 
Pal 
Sambucus Canadensis L., Cornus amomum Mill. and Cephalanthus occidentalis L. ; R, 
Sagittaria latifolia Willd. and Rudbeckia laciniata L. 
flat area of country; (2) swamps due to underground springs ; 
(3) swamps due to the collection of the drainage water of an 
area into a natural basin-shaped depression. True sphagnum 
bogs are not represented in southeastern Pennsylvania. This 
