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 Chcristocarpacece appear to be 

 related to the Sphacelariacece, while the type of re- 

 productive organs points more to the Ectocarpacece. 



The Geographical Distribution of this small order, 

 consisting of the three genera named (Pleurocladia , 

 with two species, the others with one each) is very 

 limited. Pleurocladia 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. 



ECTOCARPACE.E. 



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 Thalhcs. The primary creeping filament 

 grows by division of the terminal cell or cells and 

 bears in the most simple cases (e.g.. Streblonema) only 

 reproductive organs and hyaline hairs with basal 

 growth, or tufts of erect filaments (e.g., Ectocarpus), 

 which grow by intercalary divisions without a 

 definitely localised growing-point. These divisions 

 are at first fairly general throughout the filament ; 



