THALLOPHYTES 267 



usually of four cells arranged in a row. Each cell is capable of 

 forming a new colony. There are no gametes. 



Pediastmm (Fig. 120, 6) consists of four, eight, sixteen or 

 occasionally of thirty-two cells arranged in a plate-like colony. 

 Tt reproduces by both zoospores and gametes. 



Hydrodictyon has the cells arranged in the form of a net 

 and is known as the water-net. It reproduces by means of 

 zoospores and isogamous gametes. 



The Euglena belongs to a group of algse known as Flagellates 

 which are somewhat anomalous. They differ from certain uni- 

 cellular animals primarily by possessing chlorophyll. They are 

 aquatic and move by means of one or two (occasionally more) 

 cilia. The protoplasm is either naked or covered with a cell 

 wall which usually resembles the cell wall 

 of the animal (i.e., non-cellulose). They 

 also have a contractile movement and take 

 in food in a manner similar to the related 

 forms of animal life. They reproduce by 

 cell division. They have chlorophyll and 

 form-resting spores very similar to many FlG- 

 of the related plants. 



The order Confervales consists of multicellular, simple or 

 branched filaments, or flat thallus structures. Reproduction is 

 both non-sexual and sexual and the zoospores are ciliate. The 

 sexual reproduction ranges from isogamy to heterogamy with 

 distinct oogonia and antheridia. The zygospores may produce 

 new plants directly or zoospores, but the oospores always produce 

 zoospores. Some of the most common genera are Uloihrix, 

 Cladophora, (Edogonium and Coleochcete. 



Ulothrix (Fig. 121, a e) is a very common filamentous, iso- 

 gamous form. The cell at one end of the filament is differenti- 

 ated into a holdfast by which the plant is attached. The other 

 cells are in the form of short cylinders and uninucleate. Any 

 cells may produce zoospores, which resemble the cells of the Vol- 

 vocales. The large zoospores are four-ciliate and after swim- 



