444 BOTANICAL GAZETTE [DECEMBER 
and needs some comments (fig. 75). The physical conditions 
upon the dikes are plain. The situation is a particularly well- 
drained one, but on the outer face of those exposed to the sea 
there must be more salt than upon the inner faces, due to the occa- 
sional wash of the sea at high tides during storms. At all events 
especially on the more exposed dikes, the outer slopes usually 
show amore halophytic facies than the inner. On both faces 
there is a distinct zonation, which differs somewhat in different 
places, but appears most characteristically, especially on dikes 
exposed directly to the sea or lower courses of the tidal rivers, 
Y . rh SS 
° As : « 
ee sf ¥ 
Fi AY . Ry &. oe £ NS | + v g 
5 SIRES "es are oe uae g 
&§&8F S§ S88 wS% FSS eee 8 F 
&¥ FF SPT CK BS eve FF 
Sphagnetum Evicetum Caricetum Aspidetwn Macrospartinetum Phieumetum Staticelum Saltcornetum Spartinetum 
ie 3a 
Se [ Ks 
s, - 
~. 
~ 
- 
a 
~ a 
Ss 
Fic. 16.—Diagram to show the distribution of the principal associations and of 
their prominent species in relation to the amounts of water and salt. The species 
curves show the approximate range of the forms within one another’s habitat. The . 
two members of the Macrospartinetum can endure some salt; hence their extension 
nd it of the Spartinet ts the “‘sedge-bog.” 
as here represented. Theseco 
f 
to be as follows: On the outer face, the lowest zone, occupying 
the angle, is usually the Statice, but is sometimes Puccinellia ; 
above this is a zone of Hordeum and above this the couch, the 
almost invariable dike grass, here evidently fully at home. 
Occasionally Atriplex occurs between Hordeum and couch. 
Now the Statice is the usual marginal member of the Staticetum, 
while the Hordeum comes in early upon that formation when 
maturing and the couch comes upon it later. There is plainly 
then upon the outer face of the dikes a general repetition of the 
order in the association, though the Spartina juncea is not, as far 
as I have noticed, in its place between Statice and Hordeum. 
The zonal arrangement, however, often shows Atriplex in place 
of the Statice, and the Hordeum may be wanting. On the inner 
face of the dikes, there is usually a band of Atriplex at the lower 
angle, especially when, as is usually the case, there is a row of 
