116 SEAWEEDS 
stalk-cell may proceed to form another, as in Sphace- 
lariacece. In vegetative propagation and in the 
growth of the thallus—viz., the absence of intercalary 
growth in length—the Choristocarpacea appear to be 
related to the Sphacelariacew, while the type of re- 
productive organs points.more to the Hetocarpacew. 
The Geographical Distribution of this small order, 
consisting of the three genera named (Plewrocladia, 
with two species, the others with one each) is very 
limited. Plewrocladia is purely fresh-water, one 
species occurring near Berlin, the other in Kerguelen 
Land, while the other genera are both marine and 
confined to the Mediterranean. 
EcTOCARPACEA. 
General Characters—The thallus of the Ectocar- 
pacece is always of simple character and commonly 
consists of erect, simple or branched filaments spring- 
ing from a creeping filament or flat layer, or it may 
be reduced to a creeping filament or layer, from 
which the reproductive organs spring. These are 
both unilocular and plurilocular sporangia. 
The Thallus—The primary creeping filament 
grows by division of the terminal cell or cells and 
bears in the most simple cases (¢.g., Streblonema) only 
reproductive organs and hyaline hairs with basal 
growth, or tufts of erect filaments (¢.g., Eetocarpus), 
which grow by intercalary divisions without a 
definitely localised growing-point. These divisions 
are at first fairly general throughout the filament; 
