THE GREEN ALGAE OF NORTH AMERICA 331 



3. CLADOPHORA Kiitzing, 1843, p. 262. 



Frond composed of filaments of a single series of cells, the 

 filaments branching, usually abundantly ; branching lateral, 

 but often coming to appear dichotomous in conseqence of the 

 pushing aside of the original filament by the branch ; growth 

 chiefly by division of the apical cell, subsequent division of cells 

 being rather exceptional ; branches all of the same type ; cells 

 multinucleate, the chromatophore either covering the cell wall, 

 or forming a network on it, or in the form of numerous small 

 disks ; pyrenoids several in a cell ; asexual reproduction by 4- 

 ciliate zoospores ; sexual reproduction by biciliate gametes, 

 uniting and germinating immediately ; also sometimes germi- 

 nating without copulation. 



One of the largest genera of algae, the species abounding in 

 fresh, brackish and salt water the world over; between 300 and 

 400 species have been described ; many of them so insufficiently 

 that they can hardly ever be recognized. There are few sharply 

 marked characters for distinguishing the species, it being mostly 

 a question of more or less in one respect or another. This is 

 specially true of those inhabiting fresh water, of which an al- 

 most endless list of species, varieties and forms have been 

 named, many duplicating each other, many founded only on 

 temporary stages and abnormal conditions ; a careful mono- 

 graphing of the genus would be a most valuable contribution to 

 botany, but an exceedingly difficult task. In the meantime we 

 must be contented with recording such forms as seem fairly well 

 marked, leaving it for the future to determine what are autono- 

 mous species, what states and conditions. 



Some species of Cladophora appear to be annual, some, per- 

 haps the larger number, are perennial, the frond dying down 

 almost to the base, which persists as a prostrate matted mass of 

 cells, swollen and filled with reserve material ; when new growth 

 begins, the filaments issuing from the older cells, which cells 

 may perhaps be considered as akinetes, are so distinct in char- 

 acter that if occurring separately they would pass for quite dis- 

 tinct species. Until recently there have been included under 

 Cladophora the subgeuera Acrosiphonia (or Spongomorphd) and 

 Acgagropila ; they are now more frequently considered as sepa- 

 rate genera ; while by some writers Acrosiphonia and Spongo- 



