TO I 
Ctttkria multifida ( Grev .). 
Lofoten, and here the surface-temperature of the open sea falls 
to i*5° in February; this being again the Kiel average for 
the same month. 
There is therefore a certain amount of evidence in favour 
of the view that temperature rather than light-intensity is the 
determining factor as far as the actual existence of these 
plants is concerned, and that while Cutleria vegetates at 
a mean of 16 0 , with a range of four degrees above and below, 
Aglaozonia prefers a mean of io°, with a maximum consider- 
ably over 20°, and a minimum below 3° : further, that 
a continuance of this low temperature limits the existence of 
both these plant-forms, in that it destroys the perennating 
thallus, both in the Baltic and along the Norwegian coast. 
In order to test these data, observations were attempted at 
Plymouth in January, 1898, on perennating plants of Aglao- 
zonia , both the adult thallus and also the young perennating 
plants of the first winter germinated the previous summer, 
large numbers of which were now from *5 to 2 mm. long, and 
had been growing for months at an average temperature 
of 14°. 
It is clear that in this case the action of a constant degree 
of temperature over a longer period of time than was available 
would be preferable, and the observations were not so 
successful as might have been wished owing to the difficulty 
of maintaining a constant temperature over a long period and 
at the same time maintaining general health-conditions by 
frequent change of water; and it is probable that the data 
derived from actual distribution are more likely to be correct 
than those derived from cultures in the laboratory so long as 
the difficulty of accurately imitating the natural environment 
remains. Thus, at 25°-26°, the summer maximum for Naples, 
young perennating forms remained healthy for ten days, and 
although a few died, many were alive and well after sixteen 
days. At 27°-29°, similarly, both young and old plants 
remained healthy after six days, and there seemed reason to 
believe that at temperatures below 30° Aglaozonia might 
perennate successfully. 
