single or in pairs (seldom seen unless a great deal of material is 

 examined ) . 



The infrequency with which this species develops false branches 

 gives it the general appearance of a very coarse and thick-sheathed 

 Lyngbya. 



Forming wooly, brown, tangled clots, either floating or caught 

 among submerged aquatics, especially in hard water habitats. Mich., 

 Wis. 



MICROCHAETE Thuret 1875, p. 378 

 A uniseriate non-tapering trichome with a basal heterocyst, as well 

 as intercalary heterocysts, inclosed by a firm, thin sheath; false 

 branching sometimes present; cells barrel-shaped, shorter than wide, 

 quadrate or, in a few species, slightly longer than wide; basal hetero- 

 cyst globose, the intercalary ones short- or long-cylindric with trun- 

 cate poles; sheaths firm, thin, rarely lamellated; filaments solitary or 

 in small stellate tufts attached along their basal portion to larger 

 algae or other aquatics, bent and becoming free from the substrate 

 in the distal portion of the plant. 



The occasional false branch in this genus justifies its inclusion in 

 the Scytonemataceae. Lemmermann has set aside Microchaete, 

 Aulosira, and Hormothamnion to form the Microchaetaceae. 



Key to the Species 



1. Trichomes with spirally lamellated sheaths M. spiralis 



1. Trichomes with parallel lamellated sheaths, or sheaths unlamellated 2 



2. Sheath lamellated, double, with an inner and 



an outer firm layer -- M. diplosiphon 



2. Sheath single, thinner than above, either homogeneous or lamellated 3 



3. Heterocysts at the base of the trichome only M. Goeppertiana 



3. Heterocysts both basal and intercalary 4 



4. Filaments 16-18^ wide; sheath lamellate - -M. robusta 



4. Filaments 12-14/^ wide; sheath not lamellate- M. tenera 



Microchaete diplosiphon Gomont 1885, p. 212 

 PL 127, Fig. 2 



Filaments curved or straight, appressed to substrate for but a 

 short distance; vegetative cells 3.5-6/x in diameter, 3.7-4/i, long; basal 

 heterocyst globose to ovate, TA/x in diameter, llju, long; intercalary 

 heterocysts quadrate to cylindrical; sheath lamellated and with 2 

 or more layers; filament 10-12;a wide; gonidia (not observed in our 

 collections) in a series and about the same size as the vegetative 

 cells. 



On Pithophora filaments in a slow-flowing stream. Wis. 



[541] 



