318 Myxophycece 



There are two orders of this sub-class, both of which are 

 abundantly represented in every part of the world. 



Order I. Hormogonece. Plants filamentous ; filaments simple 

 or branched, generally consisting of one or more 

 rows of cells within a sheath, attached to a sub- 

 stratum or free-floating. 



Order II. Coccogonece. Plants unicellular or colonial, com- 

 monly embedded in a gelatinous matrix, more rarely 

 free-floating. 



Order I. HORMOGONE^E. 



This order includes all the filamentous Myxophyceae. As a 

 rule the filaments consist of a simple row of cells, naked or enclosed 

 within a sheath of varied character. In some of the Oscillatoriaceae 

 and StigonemaceaB there are two or more rows of cells contained 

 within the same sheath. A simple row of cells is known as a 

 trichome, and the trichome with its enveloping sheath is termed a 

 filament. In the Scytonemaceae, Stigonemaceas, Nostocacese, and 

 Kivulariaceas heterocysts are more or less abundantly scattered at 

 intervals among the vegetative cells, and in some genera one 

 extremity of the filament is always terminated by a heterocyst. 

 The heterocysts are commonly solitary, but they may occur in 

 groups, as in some species of Tolypothrix. The filaments are 

 frequently branched, and there is often a false branch-system due 

 to the close apposition of the basal extremities of a number of 

 filaments. New filaments often arise as lateral outgrowths from 

 the vegetative cells of an older filament. The trichomes of the 

 newer filaments separate from that of the old filament, but their 

 sheaths still remain partially fused, and thus a false branch-system 

 is produced. 



Most of the Algae of this order occur attached to a substratum, 

 and they frequently form dense, felt-like patches or tough gelatinous 

 masses of various colours. Some of them form more fragile gela- 

 tinous masses of varied form, either aquatic or on damp earth, and 

 others are free-floating. 



Asexual reproduction takes place by means of hormogones, 

 and more rarely by spores. 



As a rule the trichomes are cylindrical with obtuse or narrowed 

 extremities, but in some of these Algae there is a gradual and 



