FRESH-WATER ALG.E. 9 



By swarm spores, which lack cell walls and are always motile, 

 usually provided with cilia. The sexual reproduction is of two 

 kinds : I, Conjugation, or the union of two similar or nearly 

 similar cells called isogamons gametes. These may be either 

 motile cells, as in Ulothrix, or cells of the thallus, as in the 

 Conjugatae. They join themselves together, and their con- 

 tents fuse to form a new cell, a zygote, which, after a short 

 period of rest, develops into a new plant. 2, Sex union proper, 

 or the union of two entirely different cells, one of which, the 

 male or sperm, is many times smaller than the other, the 

 female or egg heterogamous gametes. This occurs, for ex- 

 ample, in Chara. 



The Algae are found from the Arctic zone to the Equator, 

 and no genus is confined to a single latitude. We should 

 sadly miss these plants if they were all destroyed. They do 

 much to purify the atmosphere, are used to a considerable ex- 

 tent in medicine, provide food for fishes and for men, fodder 

 for cattle, and fertilization for the ground. 



The Algae are divided into classes as follows : 



CLASS I. CYANOPHYCE^E ( Schizophyceae, Myxophy- 

 ceae, or Blue-green Algae). Containing a blue coloring matter 

 (phycocyanin). Mostly in fresh water, and simple in structure. 



CLASS II. BACILLARIE^ (Diatomaceae). Containing 

 a brown coloring matter (diatomin). Universal both in fresh 

 and salt water. 



CLASS III. HETEROKONT^E (Yellow-green Algae). 

 Containing a large amount of a yellow pigment (xanthophyll). 

 The stored product of assimilation is a fatty substance. Found 

 in fresh water. 



CLASS IV. CHLOROPHYCE.E (Green Algae). Con- 

 taining only the green coloring matter known as chlorophyll. 

 The product of assimilation is starch. Very largely fresh- 

 water plants. 



CLASS V. CHARACEiE. Having a stem with nodes 

 and internodes. Sexual reproduction. 



CLASS VI. PH^OPHYCE^ (Brown Algae). Con- 

 taining a brown coloring matter, known as phycophaein. 

 Mostly marine. 



