99 
Cutleria multi fida ( Grev .). 
however not to have been investigated, the researches of 
Reinke and Falkenberg having been carried out on the 
winter-plants (cf. p. 109). 
At Antibes the isothermals for surface-temperature very 
closely approximate those of Naples, and Cutleria has here 
the same annual period. 
North Sea , Yarmouth , Heligoland. With a cold winter, 
late cold spring, and a rapid summer rise, the North Sea 
presents a variation of from o° to 18 0 ; the Heligoland curve 
averaging a degree lower on its rise than that of the western 
shore. The fall to zero is exceptional, and the mid-winter 
average for Heligoland is well over 2°, and possibly higher 
in sheltered localities. More complete data for the occurrence 
of Ctitleria in the North Sea would be of great interest, as 
from the preceding it would appear that here the high degree 
of temperature necessary to form the mature plant did not 
obtain, as a rule, throughout a sufficient length of time ; and 
this may possibly be the explanation of the fact that Cutleria 
has been found at Heligoland, but in recent years has only 
occurred in the protonematoid form as C. confervoides. 
Similarly, Cutleria is found at Yarmouth, but is not known 
to occur along the east coast until the sea at Orkney feels 
the influence of the warm Atlantic current, although Aglao- 
zonia is often common (e.g. Berwick). It is therefore probable 
that we here reach the minimum heat-supply for the develop- 
ment of the typical Cutleria-XhdMus, owing to the fact that 
the optimum degree of temperature does not obtain over 
a sufficient period in the brightest months. 
Similarly, Kiel has a still greater range, with a high 
summer temperature but very low mid-winter average, being 
below 3 0 during the winter months, and often below zero. 
This appears to limit the Aglaozonia , and neither Aglaozonia 
nor Cutleria occur at Kiel or inside the Baltic. 
Orkney and Shetland , owing to the presence of warm 
Atlantic water, show the smallest amount of annual variation, 
the characteristic feature being the warm winter ; while the 
summer maximum is only 14 0 , the winter minimum is 4°-5°. 
H 2 
