140 



BOTANY 



viz. Nemalionales, Gigartinales, Rhodymeniales, Cryptonemiales. 

 These are further divided into about twenty families. 



Order I. Nemalionales 



These are the simplest of the Florideae, and include most of the 

 fresh-water species. They are usually densely branched Algae, but 

 may develop a tubular thallus as in Lemanea and other genera. In 

 the fresh-water genera the color is usually blackish or olive instead 

 of the red of the marine genera. The commonest of the fresh-water 

 forms are Batrachospermum and Lemanea. 



an 



FIG. 109. .4, Batrachospermum vagum (X85). B, fertilized carpogonium ; an, 

 spermatium ; sp, spores developing from the carpogonium. C, Chantransia 

 macrospora, the young form of Batrachospermum sp. (X 85). D, monosporangia 

 of C. macrospora (X250). E, single monosporangium (X 500). F, germinating 

 monospores. (B, after DAVIS.) 



Reproduction. In most of the Nemalionales non-sexual reproduc- 

 tive cells are unknown, or are monospores, although tetraspores are 

 known in some of the marine genera. 



The sexual reproductive organs are the carpogonium and antheridium, which 

 are readily studied in Nemalion (Fig. 108). The carpogonium is a flask-shaped 

 cell at the end of a branch. The antheridia are groups of small globular cells 

 also at the ends of short branches. Each antheridium-cell produces a single 



