1919] Sftchell-Gardner: Mijxophyceae 89 



end cell walls. Borzi, however, has placed a species from New Guinea 

 in this genus although i1 is liut 2/l(. in diameter. 



MicrocoJeus cdiijUk us docs not conform wholly to the characters 

 of either of the two above mentioiu'd genera. It has the few trichomes 

 and diffluent sheath of a typical Hi/drocoleum but has the small 

 trichomes of a typical Microcolcus. 



Suborder 2. IIETEROCYSTINEAE nobis 



Filaments usually attachetl, at least at first, but some floating free; 

 trichomes made u]) of cells difl'ering from one another either through 

 heterocysts being present, or through trichomes ending in a hair, or 

 through both, simple or branched; branching either true or false; 

 sheath usually present, enclosing one or more trichomes, hyaline or 

 colored, homogeneous or stratified ; propagation chiefly b}' hormo- 

 gonia; resting spores present in some species. 



Heterocysteae, Hansgirg, Syst. einig. Siisswasseralg., 1884, p. 9. 



The group of the heterocysted Myxophyceae is a fairly natural one 

 and, in spite of some minor difficulties, it seems best to retain it. It 

 was instituted by Hansgirg in 1884, and received its concrete form 

 from Bornet and Flahault in 1886. Richter in 1896 (p. 274) urged 

 certain objections but Gomont in 1899 brought foi-ward certain facts 

 tending to show the misconception under which Richter labored. Later 

 writers have abandoned the group, but without substituting anything 

 satisfactory. It is true that the heterocysts are lacking in certain 

 species, but in nearly all cases, at least, there is, in such instances, a 

 hair present. In other species, heterocysts may be scanty or rarely 

 found, but all such cases show their affinities by other peculiarities 

 of structure. We have, therefore, retained the group, simply changing 

 the termination to conform with what seems to be the best usage, 



FAMILY 4. NOSTOCACEAE naeg. 



Thallus floating singly or gregariously, of definite, globular, ovoid, 

 or regularly lobate form or irregularly expanded, solid or hollow, 

 soft to firmly gelatinous; trichomes unbranched, never tapering to 

 a hair, both extremities usually similar, heterocysts present; propa- 

 gation by hormogonia and resting spores. 



Naegeli, Neu. Algensyst., 1847, p. 132 ("Nostochaceae," lim, mut.). 

 Nostoce^ae Kuetzing, Phyc. Gen., 1843, p. 203 (lim. mut.). 



