96 
Church . — The Polymorphy of 
The Relation of Cutleria to Physical 
Environment. 
i . Means of Dispersal. 
From evidence derived from floating bottles, it is clear that 
anything that will float will be carried indefinitely along the 
lines of currents and prevailing winds. 
When it is borne in mind that the spores of Cutleria and 
Aglaozonia will germinate freely on the surface and float for 
at least the first month of their existence, and that the film 
of germinating spores may be at least equal in area to the 
plant producing them, it is clear that these plants must have 
practically unlimited powers of dispersal, and that their 
presence or absence at any given spot must be solely deter- 
mined by the conditions of external environment. 
2. Relation to Temperature. 
Of the factors of external environment which influence 
the growth of marine Algae, temperature, light-intensity, the 
transparency of the water and velocity of current, the first- 
mentioned is the one most easily measured ; and beyond 
small daily and local variations on the grand annual curve 
this is so remarkably constant that it is probable that the 
sensitiveness of marine vegetation to temperature will be 
found to lie within far narrower limits than in the case of 
subaerial vegetation. Thus, although seasonal changes are 
strongly marked, the extreme annual range which at Naples 
is 20°, is only 12° at Plymouth, less than 8 ° at Shetland, and 
as little as 6 ° at points along the east coast of Scotland 
(Isle of May). The maximum temperature is found at the 
end of August, the minimum in February ; the sea thus 
undergoing a steady and rapid rise in early summer, and 
a rapid fall in late autumn. The former is accompanied by 
a great amount of light-supply during the summer solstice, 
the latter by a great diminution in light-intensity towards 
