Marshall—The Vegetation of Twin Island. 775 
point, while the west end joins the marsh. The northeastern 
portion is the highest, rising in one place rather abruptly 
about three meters. From the center the land gradually rises 
toward the north and east. 
Three well defined plant formations occur; they are desig¬ 
nated as center, back strand, and strand. The center com¬ 
prises the greater part of the island; it supports trees, shrubs,, 
and shadedoving herbaceous plants. The strand is a narrow 
belt of varying width with an average width of perhaps one 
meter, extending from the water’s edge to high-water mark,, 
the latter point easily determined by a careful examination of 
the shore-line. Owing to the fall of the surface of the water 
already noted, the strand belt became gradually wider and the 
new region was taken possession of in favorable places by 
seedlings. Here, then, was plenty of light and moisture and 
the number of plant individuals was very great. Between the 
center and the strand a narrow intermediate belt was found 
which constituted the back strand; the outer limit, the high- 
water mark, was clear, but it passed on the other side rather 
imperceptibly into the center. Hence many plants of the 
center and strand occurred here also. Outside of the strand 
in the shallow water there is a zone of variable width where 
a few strictly aquatic plants grow. Besides these general re¬ 
gions, there were two others of special interest. One of these 
is a large semicircular area of back strand, a sort of bay, on 
the south shore, about fifteen meters deep; the other is a much 
smaller oblong area near the elevated eastern point where the 
surface is devoid of trees and shrubs, and hence well exposed to* 
the light. 
TEMPERATURE RECORDS. 
Temperature records were taken with a Fahrenheit ther¬ 
mometer each day (except Sunday) between the hours of 
10 and IT o’clock a. m., of water, soil and air. The tempera- 
lure of the surface of the water was taken just outside of the 
zone of water plants, and again inside of this zone. At cer¬ 
tain stations the temperature of the soil of the south strand 
