AMPHITHRIX Kuetzing 1843, p. 220 

 Thallus composed of erect, parallel, tapering trichomes from a 

 basal pseudoparenchymatous tangle of closely appressed trichomes; 

 heterocysts and akinetes wanting; plant mass often purplish. 



Amphithrix janthina ( Mont. ) Bornet & Flahault 1886, p. 344 



PI. 131, Fig. 9 

 Characters as described for the genus; trichomes tapering to a fine, 

 hair-like extremity, composed of rectangular cells; sheaths thin and 

 colorless; cells 1.5-2.5/i, in diameter. 

 Mich. 



CALOTHRIX C. A. Agardh 1824, p. xxiv 

 Trichomes tapering from basal heterocyst (rarely wanting) to a 

 fine point in most species, abruptly ending in others. In some species 

 the lower part of the trichome is cyhndrical, only the apical region 

 tapering. Vegetative cells shorter than wide below, longer than wide 

 toward the apices; heterocysts subglobose or hemispherical, basal 

 but sometimes intercalary also; gonidia (akinetes) often present, 1 

 or more in a series, adjacent to the basal heterocyst; sheaths firm, 

 close, either homogeneous or lamellated, but not flaring away from 

 the trichome (see Calothrix adscendens); filaments usually simple, 

 sometimes with false branches from the midregion; plants either 

 sohtary or clustered to form stellate tufts, the basal portion of the 

 plant lying approximately parallel with the substrate and then bend- 

 ing away at a sharp angle (in most species); either epiphytic or 

 endophytic ( in the mucilage of other algae ) , growing on submerged 

 or on exposed and moist rock surfaces, where extensive patches may 

 be produced, sometimes becoming encrusted with lime. 



Key to the Species 



1. Akinetes present C. stagnalis 



1. Akinetes absent _ 2 



2. Filaments definitely enlarged in the basal portion; sheaths some- 

 times inflated below — 3 



2. Filaments very gradually tapering, or cylindrical throughout much 



of their length and then tapering - -- 5 



3. Filaments compactly arranged in common mucilage, forming a 

 colonial expanse on aquatic substrates C. Braunii 



3. Filaments solitary, or in small tufts, intermingled among other 



algae, or epiphytic "* 



4. Sheath close, without lamellations; scattered among 



other algae -- - C. stellaris 



4. Sheath wide, lamellated; plants attached in the mucilage 



of other algae ^ • /"*ca 



[551] 



