Marshall—The Vegetation of Twin Island. 779 
surface in the large semicircular area of back strand on the 
south side at the foot of a small poplar was registered for a 
week in mid-August. These records were not kept regularly; 
hut on August 20, the day preceding the hottest day of the 
summer for the region, the mercury at 10 :00 stood at 91%°'. 
Other records for the first week of August show that the soil 
surface temperature on the southwest back strand ranged from 
58° at 9:00 to 92° at 1:00 o’clock. These shorter records 
therefore go to show that the range of temperature would he 
considerably greatest if records throughout the day were kept. 
It will he noticed that the highest temperature was reached 
in mid-August. Upon the south strand other conditions were 
especially favorable for vegetation; the zone is here wide, and 
the retreating water added nearly two meters to it during the 
summer. Water is abundant and the exposure favorable for 
light. The characteristic plants here were marigolds ( Bidens ) 
which flower in late summer. 
A low soil temperature is a striking fact brought out by these 
records, a temperature lower than that of the water. This may 
be accounted for in part by the fact that the south channel is 
shallow water and hence heats rapidly; but a more important 
factor is the low temperature of the air. The last two weeks 
of June, before records were taken, had been very cool days 
with heavy rains. From then on the rainfall for two months 
was slight, an almost unbroken record of clear days. On the 
night of July 14, however, a heavy rain storm occurred and 
all temperature records on the following day showed a decided 
drop. Cloudy days and light rains came in late August; the 
next heavy rain was not until September 1. 
VEGETATION OF THE CENTER. 
The center, the largest formation, presented the greatest 
diversity of conditions and the largest number of species. The 
area of the center comprises all of the island except the two 
bordering narrow zones of back strand and strand. Its charac¬ 
teristic plants are trees and shrubs, the latter increasing in 
number toward the outside and forming a fringe which runs 
into the back strand zone. Toward the western end the surface 
