172 



FRESH-WATER BIOLOGY 



249 (68, 190) Plants of non-septate, branched filaments, forming felt-like 



masses on water or earth; or plants minute, growing on the 

 surface of moist earth or in the tissues of higher plants; 

 nuclei, many. Reproduction by zoospores, isogametes, or 



heterogametes Order Siphonales . . 250 



Many marine forms; fresh water forms few, differing greatly, "in appearance and reproduction. 



250 (251, 252) Plant a felt-like mass of branched filaments which contain no 



septa except when reproductive bodies are formed. 



Vaucheria de Candolle. 



Plant branched; chromatophores nu- 

 merous, parietal, disc-shaped; asexual 

 reproduction either by zoospores or by 

 akinetes, the former borne singly in ter- 

 minal sporangia, the latter occurring as 

 spherical cells on short, lateral branches; 

 oogonia, each containing one oosphere, and 

 antheridia, each with many antherozoids 

 are borne side by side either laterally or 

 on the ends of short branches. 

 FIG. 242. Vaucheria repens Hassall. X 300. 

 (Original.) 



251 (250, 252) Plant growing on moist earth, about i mm. broad, erect, green, 



balloon-shaped, with branched, colorless rhizoids at smaller 

 end. Botrydium Wallroth. 



Chromatophores numerous, minute, parietal, each with a pyre- 

 noid; reproduction by zoospores; under dry conditions resting spores 

 may be formed in the branched rhizoid-like organ of attachment. 



FIG. 243. Botrydium granuiatum Greville. X 15. (After Goebel and 

 Woronin.) 



252 (250, 251) Plants growing on the tissues of higher plants. 



253 (i) 



Plants parasitic in the leaves and stems of aquatic 

 plants. The lower end is inflated, green, the upper part 

 colorless. In the vegetative part the chromatophores are 

 indistinct. Reproduction by internal division or aplano- 

 spores which are liberated by the rupturing of the cell wall. 

 In these the chroma toph ore is distinct. 



FIG. 244. Phyttosiphon arisari Kiihn. Cells of host not shown. 

 X 40. (After Just.) 



Plant coarse, at least several centimeters long, with a linear, cylin- 

 drical, occasionally branched axis, showing nodes and inter- 

 nodes; at the nodes, whorls of cylindrical leaves which in 

 turn bear leaflets; sometimes encrusted with lime. Growth 

 a P ical ................ Order Charales. 



Only one family ............ CHARACEAE . . 254 



