io6 Church. — The Polymorphy of 
form, giving (i) a further specialization of the shoot-system in 
Stypocaulon and Cladostephus ; (2) a suppression of the shoot 
system, and reduction to the creeping dorsiventral disc alone 
in Battersia. Such a reduction to a dorsiventral creeping 
thallus is again in Algae, from a vegetative point of view, 
a distinctly down-grade specialization. The plant, by adopt- 
ing a prostrate habit, exposes far less assimilatory surface to 
the action of light and free-flowing currents which bring both 
food and oxygen supply ; on the other hand, it gains in the 
struggle to resist the tensions and tractions of wave motion, 
and will thus exist safely, not only throughout more stormy 
seasons, but farther up towards the tide-mark. 
The relation of Cutleria to Aglaozonia , from a vegetative 
point of view, is simply that the two growth-forms represent- 
ing the extreme cases of specialization of such types as Clado- 
stephus and Battersia are here combined in a single species, 
and become fixed, one way or the other, at a very early stage. 
Thus it is interesting to note that the delicate Cutleria- thallus 
is confined to comparatively quiet waters and depths at least 
two fathoms below low-tide mark, and possesses a very slender 
point of attachment in relation to the bulk of the full-grown 
thallus ; while Aglaozonia rises, from equal depths, to rocks 
even above the tide-mark in many localities (Sidmouth). 
Further, accompanying feeble powers of growth and nutri- 
tion, and possibly correlated with them, Aglaozonia possesses 
an increased power of withstanding extremes of temperature. 
Beyond the ‘ massive ’ stage, the Cutleriaceae make one 
more advance, which forms the unique characteristic of the 
order. This consists in the fusions which take place between 
the axes produced from the independent filaments of the apex 
of the thallus, leading to a fasciated growth which further 
presents the complication of dorsiventrality. That this is 
not only the essential feature of the Cutleriacean type, 
but is the last and most recently acquired and there- 
fore most mobile character, is suggested by the following 
considerations. 
(1) The specific characters are essentially based on the 
