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 amcng 
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 may be observed in various stages of di vision, 
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 
among 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 
FIG. s.-Merismopedia: a por- J rem ^ably regular rectangular colony (fig. 5). 
tion of a colony, showing the one- II 1S CVldent that thls r ^ ctan g ular form ls deter - 
celled plants in rectangular arrange- mined b ? a s 6 " 63 of Perfectly regular and 
ment, and all held together by the simultaneous divisions in two directions, 
gelatinous matrix; in one case cell- 
division has not been completed. Oscillatona. 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 
