PROTOPHYTA 61 



less membrane, but in many cases this membrane is conspicuous 

 because of markings, ridges, flanges, etc., or is thickened by the 

 deposit of silicious or calcareous plates. Cups (or houses) and 

 stalks, usually of cellulose, secreted by the organisms themselves, 

 are not uncommon. 



Sexual processes are entirely unknown in this class, reproduc- 

 tion occurring by the longitudinal division of the cells. The 

 daughter cells in many cases become independent after division, 

 but there is a tendency in the group for the cells to remain con- 

 nected in one way or another so as to form colonies. Sometimes 



Fig. 32— SYNURA UVELLA 



A colony of yellow-colored flagellated 

 cells which are attached by their inner 

 ends. Each cell has two flagella 

 and two chromatophores. Synura is 

 a frequent cause of a "cucumber- 

 like" odor in drinking waters 



From a photomicrograph by the author 

 Magnification, 600 



they remain associated side by side, thus forming catenoid col- 

 onies; or they remain attached by stalks or cups and form branch- 

 ing or arboroid colonies; or they may remain embedded in a 

 gelatinous matrix, thus forming spheroidal colonies. 



Many of the Chrysophyceae have the ability to discard their 

 flagella, round out, secrete a jelly and pass into a palmella stage, 

 during which reproduction takes place. In some types this is 

 only temporary, the active phase being quickly resumed. In 

 others, however, this palmella stage is the dominant phase {e.g., 

 Hydrurus, Fig. 20, page 50), and the resemblance to higher 

 types of algae is obvious. 



The power of encystment is also characteristic. In this proc- 

 ess a monad withdraws its flagella and secretes an impervious 

 membrane, within which it is protected against adverse en- 



