432 



A TEXTBOOK OF BOTANY 



[Cn. X 



The marine forms include Caulerpa (Fig. 300), which 

 exhibits a differentiation into apparent stems, rhizoids, and 

 leaves; these structures, however, are very different mor- 

 phologically from their analogues in the higher plants. The 

 protoplasm in these huge coenocytes shows very active 

 streaming movements, the most active known (viz. about 

 10 mm. per minute, as against 3-5 in Chara) ; and so large 

 are the tubular compartments that they would apparently 



suffer collapse were it not 

 for the system of cross 

 beams which many of them 

 possess. Others have beau- 

 tiful feathery fronds (Bry- 

 opsis), and some kinds 

 exhibit striking umbrella- 

 like shapes (Acetabularia) . 

 The latter, and some others, 

 are heavily incrusted with 

 lime. ; 



Ecologically the Siphon- 

 ales are mostly marine hy- 

 drophytes, though the few 

 of fresh water live also 

 on land. Phylogenetically 

 they seem clearly related to Confervales, from which 

 they differ chiefly in absence of cross septa, and of which 

 they are no doubt an offshoot, specialized in the reproductive 

 mechanism. 



ORDER 5. CHARALES : THE STONEWORTS. These are slender- 

 jointed, whorled-branching, green growths, a foot or more 

 long, rising from the bottoms of ponds, often over consider- 

 able areas. Some kinds are incrusted with lime and are 

 brittle and rough, whence their common name. They occur 

 only in fresh water, and include some 160 species, none of 

 which have economic uses. 



FIG. 300. Caulerpa prolifera ; X 

 (From Oltmanns.) 



