CHAPTER IV. 



SUB-KINGDOM II. 



IN the second sub-kingdom of plants is embraced an enor- 

 mous assemblage of plants, differing widely in size and com- 

 plexity, and yet showing a sufficiently complete gradation from 

 the lowest to the highest as to make it impracticable to make 

 more than one sub-kingdom to include them. They are nearly 

 all aquatic forms, although many of them will survive long 

 periods of drying, such forms occurring on moist earth, rocks, 

 or the trunks of trees, but only growing when there is a 

 plentiful supply of water. 



All of them possess chlorophyll, which, however, in many 

 forms, is hidden by the presence of a brown or red pigment. 

 They are- ordinarily divided into three classes I. The Green 

 Algae (Chlorophycece) ; II. Brown Algae (Phceophycece) ; III. 

 Bed Algae (Rhodophycece) . 



CLASS I. GREEN ALG^;. 



The green algae are to be found almost everywhere where 

 there is moisture, but are especially abundant in sluggish or 

 stagnant fresh water, being much less common in salt water. 

 They are for the most part plants of simple structure, many 

 being unicellular, and very few of them plants of large size. 



We may recognize five well-marked orders of the green algae 

 I. Green slimes (Protococcacece) ; II. Confervacece ; III. Pond 

 scums (Conjugatce) ; IV. Siphonece; V. Stone-worts (Characece) . 



1 Algae (sing. alga). 21 



