Postelsia 17 
not growing in the Phvyllospadix association, is 
Zostera marina. It is found only in the sheltered 
coves of the inner San Juan Harbor and in these 
places it grows from a muddy or sandy bottom, 
where its blades at high tide reach up through 
the water somewhat after the fashion of Val- 
lisnerta spiralis. That it occurs to some extent 
on the Washington side of the straits is shown 
by the fact that not infrequently it is washed in 
after heavy winds from that direction. It does 
not grow in such great masses as Phyllos padix 
scoulert. 
Il. Formations of the beach. 
The area occupied by the beach formations 
varies with the varying contour of the shore. In 
some places the distance between wave-washed 
rock and forest edge may be only a few meters, 
with scattered crevice plants established upon 
the narrow ground. In other places the inter- 
vening space may be a hundred meters or more 
wide, made up either of a sloping sand beach, 
smooth in front but riddled with drift wood 
towards the back, or formed of tilted strata 
supporting a crevice flora of varying aspect, which 
