THE MARINE ALG^E OF NEW ENGLAND. 185 



ARTIFICIAL KEY TO GENERA. 



Note. — The following key is intended to enable persons who are not at all acquainted 

 with our sea-weeds to ascertain with a partial degree of accuracy the genera to which 

 specimens which they may collect are to be referred. For this purpose the characters 

 used are, as far as possible, those which can be seen by the naked eye, but, as in many 

 cases, the generic distinctions absolutely depend on microscopic characters, one must 

 not expect to be able to recognize all of our forms without making a more or less care- 

 ful microscopical examination, especially in the case of the Cryptophyceos and Phceo- 

 sporcw. It should of course be understood that the key is entirely artificial, and does 

 not represent the true botanical relations of our genera ; since in many cases the char- 

 acters refer only to species of our Atlantic coast and would mislead a student having 

 a specimen from other waters. 



1. Color bluish or purplish green,* algss of small size, usually more or 



less gelatinous c ( Crytopliyceri) 5 



2. Color grass green 18 



3. Color from yellowish brown to olive green or nearly black 26 



4. Color red or reddish purple, rarely blackish, in fading becoming at 



times greenish (Floridece) 48 



5. Cells arranged in filaments 9 



Cells in colonies, but not forming filaments G 



G. Cells grouped in twos or some multiple of two 7 



Cells solitary, not adherent in twos 8 



7. Groups free, not united with one another by a gelatinous envelope. 



Chroococcus. 



Groups united by a gelatinous substance so as to form irregularly- 

 shaped colonies Glceocapsa. 



Groups united by a gelatinous substance so as to form colonies of a 

 dendritic shape Entophysalis. 



8. Cells imbedded in a gelatinous substance, forming colonies of indefi- 



nite shape Polycystis. 



Cells imbedded in a gelatinous mass, which forms at first ovoidal and 

 afterwards net-shaped colonies Clathrocystis. 



9. Filaments ending in a hyaline hair 1G 



Filaments not ending in a hair 10 



10. Filaments provided with heterocysts t 11 



Filaments destitute of heterocysts 12 



11. Filaments with a thin gelatinous sheath, spores not adjacent to the 



heterocysts JSfodularia. 



* Our marine species of Clathrocystis and the genus Beggiatoa are exceptions. The 

 former is pinkish, and covers the mud and algae between tide-marks with a very fine 

 gelatinous film. The species of Beggiatoa are whitish to the naked eye, and form very 

 delicate films over decaying algae. 



t Vid. page 11. 



