10 MORPHOLOGY 



Stigonema. In some Cyanophyceae, however, true branching occurs, and 

 this is illustrated by such forms as Stigonema, in which branches are started by 



lateral outgrowths from individual cells of the 

 filament rather than by mechanically freeing 

 some of the cells (fig. 12). 



Conclusions. A brief summary of the 

 important features of the Cyanophyceae 

 may be stated as follows: 



(i) The plant body is a single cell, 

 and the general tendency is to organize 

 a colony of cells into the form of a simple 

 filament. 

 FIG. 12. Stigonema: showing ( 2 ) Tnere j s a characteristic mucilagi- 



true branching. After BORZI. . f . ,, !_ i. r 



nous swelling of the walls, which favors 

 colony formation by imbedding the individual cells. 



(3) The protoplast is apparently simple in organization, giving no 

 evidence of distinct chloroplasts, and with a nucleus ordinarily not 

 sharply limited by a membrane, both of which features are in contrast 

 with the protoplasts of true algae. 



(4) There is some differentiation of cells, notably in the formation 

 of heterocysts; and differentiation reaches its extreme expression in 

 such forms as Rivularia, with base and apex. 



(5) The power of locomotion is evident in the group, notably in 

 Oscillatoria, and also in connection with colonization by means of hor- 

 mogonia. 



(6) The only method of reproduction known is vegetative multipli- 

 cation, and the cell divides by an ingrowing wall plate. 



(7) Protection ae^inst unfavorable conditions is provided for by 

 the transformation or ordinary vegetative cells into resting cells, the 

 chief changes being enlargement, accumulation of reserve food, and a 

 heavy wall. 



(2) SCHIZOMYCETES 



General description. The name means fission fungi, and corresponds 

 in form tc Schizophyceae (fission algae), a name often applied to the 

 blue-green algae. However, they are best known as bacteria. The 

 group has many characters in common with the Cyanophyceae, such as 

 the one-celled body which often forms filaments (colonies), a protoplast 

 of simple structure, the tendency in certain conditions to produce a 

 mucilaginous matrix that embeds the cells, the power of locomotion, and 



