48 BOTANICAL GAZETTE [JANUARY 
reef rim. As one approaches the lagoon, wading is no longer pos- 
sible, the water is 3-10 m. or more deep, but again becomes shal- 
lower as the outer edge of the reef is reached. The water of the 
lagoon is placid, clear, and very transparent, so that the bottom 
receives good illumination. Although a number of the smaller 
algae grow upon the floor of the lagoon, the region is comparatively 
barren as compared with the shallower waters on either side. The 
lagoon floor is a region of coralline and animal life, rather than of 
the larger plant life. The quantities of sand that are constantly 
washed over the floor from the disintegrating reef rim render it 
difficult for plants to maintain themselves. Probably if conditions 
for collecting on the lagoon floor were more favorable, a larger 
number of species would be found than are apparently present. 
5. Reef rim.—Upon rowing across the lagoon to the outer rim 
of the reef, one comes to shallow water, where the surf breaks, and 
where wading is possible. This zone is a favorite fishing ground 
of the native Hawaiians, and it abounds with both animal and plant 
life. The highest portions of the rim may be practically exposed 
at low tide, although at high tide they will be covered by 18-24 
inches of water. The rim of the reef is by no means regular or 
symmetrical; there are many indentations, crags, débris slopes, 
pools, hummocks, and sandy spots all along the outer margin. 
Almost all of the visible coral in this region is living coral, asso- 
ciated with an abundance of corallines, bryozoans, hydroids, red 
algae, and other forms of life. Some of the algae that are confined 
largely to the outer reef rim are Haliseris, Dictyota, Codium, Aspara- 
gopsis, Gymnogongrus, Porphyra, Turbinaria, Gelidium, etc. Many 
of the species that inhabit these surf-churned waters are not the 
tough, cartilaginous forms, but very delicate and fragile species, 
that apparently survive the wave action because of their very 
delicacy. This is particularly true of some of the finer red algae. 
TIDES 
The situation of the Hawaiian Islands, in the great stretches 
of the North Pacific, is such that the tides are very small; in con- 
trast with the tides usual along continental coasts they are exceed- 
ingly small. The average rise and fall lies within a vertical range 
