strongly curved and twisted, sometimes club-shaped, with a narrow, 

 stipe-like base, 3.8-4/a in diameter, 14-65^ long. 

 Growing on Drepanocladus in deep water ( 5-15 m. ) . Wis. 



Chamaesiphon incrustans Grunow in Rabenhorst 1865, p. 149 



PL 108, Figs. 7, 8 

 Cylindrical, gregarious, usually straight (sometimes slightly 

 curved), attached to filamentous algae or leaves of aquatic plants; 

 cells 3-6-(8))u. in diameter, 10-25 ju, long. 



This plant was found growing on mosses and other vegetation 

 taken from a depth of 30 feet. Mich., Wis. 



ORDER HORMOGONALES 



In contrast to the Chroococcales and Chamaesiphonales, plants 

 in this order are filamentous, comprising a "tribe" known as the 

 Hormogoneae, the other orders making up the "tribe" Coccogoneae. 

 The plant may consist of a trichome of cells inclosed by a sheath 

 which is extremely variable in character, or there may be no sheath. 

 In one suborder, the Homocystineae, there is no differentiation of 

 the cells within the trichome, and, also, there may or may not be 

 basal-distal differentiation. In the other suborder, the Heterocy- 

 stineae, there is a specialization of certain cells in the filament to 

 form two types of structures which are of taxonomic value. One of 

 these is the heterocyst, a thick-walled cell, usually somewhat larger 

 and often different in shape from the vegetative cells. The contents 

 are ordinarily homogeneous. In many cells, the wall at either pole 

 is thickened by a plug of mucilage. The heterocyst may be terminal 

 only, intercalary, or lateral to the trichome. Another special cell 

 is the spore or gonidium, sometimes termed akinete. This cell is 

 usually much-enlarged and thick-walled and has an adventitious 

 reproductive function. 



The presence or absence of the heterocyst and spore, the position 

 of these in the trichome, together with form and size, are all- 

 important in the recognition of species in this order. Heterocysts 

 are incapable of cell division, but they assist in vegetative repro- 

 duction by facilitating fragmentation of the trichome, or by deter- 

 mining points of proliferation of the trichome through branch for- 

 mation. In some forms heterocysts are known to function as spores. 



Branching of the trichome may be false, or there may be true 

 branching as a result of cell division in two planes. Reproduction 

 by fragmentation of the trichome to form hormogonia is common 

 to nearly all forms, whereas gonidia are employed only in certain 

 families or genera. 



[477] 



