CHAPTER XVIII. 



CLASSIFICATION AND ADDITIONAL STUDIES OF 

 THE ALQyE. 



In order to show the general rchitionship of the algae stndied, the princi- 

 pal classes are here enumerated as well as some of the families. In some 

 of the groups not represented by the examples studied above, a few species 

 are described which may serve as the basis of additional studies if desired. 

 The principal classes * of algce are as follows: 



Class Chlorophyceas. 



331. These are the green alga\ so railed because the chlorophyll green 

 is usually not masked b}' other pigments, though in some forms it is. There 

 are three subclasses. 



332. Subclass PROTOCOCCOIDE.a;.— In the Protococcoidea: are found the 

 simplest green plants. Many of them consist of single cells which live an 

 independent life. Others form ''colonies," loose aggregations of indi\'id- 

 uals not yet having attained the permanency of even a simple plant body, 

 for the cells often separate readily and arc able to form new colonies. The 

 colonies are often held together by a gelatinous membrane, or matri.x. 

 Some are motile, while others are non-motile. A few of the families are 

 here enumerated. 



333. Family Volvocaceae. — These are all motile, during the vegetative 

 stage. The individuals arc single or form more or less globose colonies. 



334. The "red snow" plant (Sphserelia nivalis^. — This is often found in 

 arctic and aljiine regions lorming a red covering over more or less large 

 areas of snow or ice. P'or this reason it is called the ''red snow plant." 



335. Sphaerella lacustris, a closely related species, is ven- widclv dis- 

 Iributeil in temperate regions along streams or on the borders of lakes and 



* In Engler & Pranll's Pnanz.enfamilien, Willc uses the term class for 

 these principal subdivisions of the alga'. Systcmatisls arc not yet agreed 

 upon a uniform use of the terms. 



15S 



