HOW TO KNOW THE FRESH-WATER ALGAE 



Figure 197 



The firmness of the mucilage in which the plants are encased differ- 

 entiates Chaetophora from its relatives Draparnaldia (Fig. 197) and 

 Stigeoclonium (Fig. 177). 



280a Thallus composed of slender, repeatedly branched filaments; cells 

 all about the same size but tapering to fine points or hairs. See 



Fig. 177 STIGEOCLONIUM 



280b Thallus consisting of an axis of large cells from which arise tufts 

 of branches composed of smaller cells; tufts in whorls, opposite 

 or alternate, occurring at rather regular intervals. Fig. 197.... 



DRAPARNALDIA* 



Fig. 197. Draparnaldia glomerata 

 (Vauch.) Ag., showing tufts of lateral 

 branqhes, with barrel-shaped axial 

 cells containing band-like chloro- 

 plasts. 



The genus is strikingly characterized 

 by having a filament of large cells 

 forming an axis from which tufted 

 branches of smaller cells arise. Differ- 

 ent species vary in size and shape of 

 branching tufts. The thallus is inclosed 

 in amorphous mucilage. Most species 

 occur in cold water, often in shallow 

 trickles or in springs. Macroscopically, 

 they appear as pale green gelatinous strands that easily slip through 

 the fingers. 

 281a (241) Parasitic in higher plants such as Arisaema (Indian turnip). 



See Fig. 92 PHYLLOSIPHON 



281b Not parasitic 282 



282a Filaments repeatedly dichotomously branched, regularly constrict- 

 ed at the base of the forkings. Fig. 198 D1CHOTOMOSIPHON 



Fig. 198. Dichotomosiphon tubero- 

 sus (Braun) Ernst. 

 This species (the only one in the 

 genus) occurs in dense, entangled 

 tufts or mats, usually on the bot- 

 tom of lakes, although occasional- 

 ly on damp soil. There are down- 

 ward growing, rhizoidal branches 

 and upward directed vegetative 

 Figure 198 anc j sex organ-producing branches. 



The oogonia when mature are so large that they can be easily seen 

 with the naked eye. The plants seem to reproduce sexually only 

 when growing in relatively shallow water (up to 4 feet) but may 

 form extensive mats on the bottoms of lakes without fruiting in water 

 up to 60 feet in depth. 



* Draparnaldiopsis is a rare genus resembling Draparnaldia but differs essentially 

 by having long and short cells in the main axrs (alternating). Tufts of branches are 

 given off by the short cells only. 



123 



