Ch. XIV] THE HYDROPHYTES 563 



The limitations of this book do not permit consideration of 

 details, which often include remarkable adjustments in 

 minutiae, not only of structure, but also of physiology. 



Free-swimming Micro-hydrophytes ; unicellular, ovoid, 

 thin and smooth walled, actively locomotive with cilia or 

 flagella; typified by some Flagellates (Fig. 280), Chlamy- 

 domonas (Fig. 284), and by zoospores, gametes, and sperma- 

 tozoids of Algae. Allied are colonial forms of Volvox (Fig. 

 288). Drifting Micro-hydrophytes; unicellular, glob- 

 ular or radiate, often thick-walled, carried in suspension 

 by currents; typified by Peridinece (Fig. 281), Desmids and 

 some Diatoms (Figs. 295-6), and by non-motile spores of 

 Algae and Fungi. Allied are some filamentous forms, 

 and non-motile colonies, like Pediastrum (Fig. 286), and 

 Hydrodictyon (Fig. 287) which is simply an overgrown form. 

 Allied are the Water Blooms (page 401), including the famil- 

 iar floating felts of Spirogyra (page 425). Drifting Sea- 

 weeds; chiefly brown Rockweeds, originally attached but 

 now drifted by ocean currents, vegetatively reproducing; 

 typified by Sargassum (Fig. 309), which fills the Sargasso Sea. 

 Adherent Micro-hydrophytes ; unicellular, gelatinous- 

 walled, and thus adherent to one another and the substratum ; 

 typified by many Cyanophycece (Fig. 276), and Pleurococcus 

 (Fig. 285). Since these gelatinous walls progressively resist 

 increasing loss of water, and also absorb it eagerly when 

 offered, these forms can survive when exposed to air, and 

 can even occupy dry situations, thus becoming aerophytic 

 and even xerophytic. Allied are the forms of the tubular 

 Algae, e.g. Vaucheria (Fig. 298) and Botrydium (Fig. 299). 

 Sedentary Filar-hydrophytes; filamentous, attached by 

 holdfasts, and rising buoyantly towards the light, often 

 social, in pilose masses; typified by Ulothrix (Fig. 289) 

 and other Confervoid Algae, and by colonial Desmids and 

 Diatoms. The Characece (Fig. 301) and the marine Siphon- 

 ales are overgrown forms. Frondose Seaweeds ; thalloid, 

 but thin or finely cut, attached by holdfasts, and rising 



