MORPHOLOGY 



evident, and represents all the organization that has been found in this 

 group. This apparently simple structure of the protoplast is in striking 

 contrast with that found in the true algae and in all higher plants. 



The division of the cell is of equal simplicity, for it takes place by 

 the development of a ringlike wall which grows inward and cuts the 

 protoplast in two, the central body (or nucleus) also playing a part. 

 This process of cell-division is the only method of reproduction among 

 the Cyanophyceae, a method known as vegetative multiplication, and 

 meaning that an ordinary working cell (individual) divides and forms 

 two new individuals. 



In Gloeocapsa the cells maybe observed in various stages of division, 

 but the multiplying cells (individuals) are held together mechanically 

 in a gradually accumulating gelatinous matrix (fig. 4), this swelling 

 mucilaginous material being derived from the cell walls, which are 

 being renewed constantly from within by the protoplast. This forma- 

 tion of mucilage by the walls and the imbedding of cells is characteristic 



of the Cyanophyceae. These groups of 

 cells held together mechanically are 

 spoken of as colonies. In Gloeocapsa the 

 colonies are irregular and indefinite, but 

 "IA^PtI^Sm^MwIC ^""""g other Cyanophyceae they will be 



observed to assume very definite forms. 



Merismopedia. — In this form, very common 

 in ponds, the cells are arranged so as to produce 

 a remarkably regular rectangular colony (fig. 5). 

 It is evident that this rectangular form is deter- 

 mined by a series of perfectly regular and 

 simultaneous divisions in two directions. 



Fig. 5. — Merismopedia: a por- 

 tion of a colony, showing the one- 

 celled plants in rectangular arrange- 

 ment, and all held together by the 

 gelatinous matrix; in one case cell- 

 division has not been completed. 



Oscillatoria. — In this well-known form 

 the colony has become a simple filament, 

 and the mucilage sheath is so thin as to be visible only in specially 

 prepared sections (fig. 6). In the related Lyngbya the sheath is quite 

 evident. In these forms a filament is built up because the successive 

 cell-divisions are all in the same direction. Each cell of the Oscil- 

 latoria filament, excepting the end ones, has the form of a short 

 cylinder, indicating that the ends of each cell have been flattened by 

 the pressure of the contiguous cells. At the end of the filament the 

 free surface of the end cell is seen to be convex; and where some cell 

 in the filament has become destroyed, as mentioned below, the adjacent 



