CEDOGONIUM 217 



seen immediately below the striae : note its form and connexion 

 with the cell-wall ; also, when seen in optical section, a central, 

 dark mark : it is here that the ring splits, and by stretching of 

 the ring the well-known process of intercalation of a new zone 

 of cell-wall follows. Examine actively-growing filaments, and 

 try to observe various stages of this peculiar process, noting 

 also any indications of the cell-division which follows it, the 

 new septum being formed immediately below the thin-walled 

 intercalated zone. 



Passing to the examination of the cell-contents, observe 



1. The colourless protoplasmic basis, in which are em- 

 bedded 



2. The chromatophores, which appear as elongated and 

 branched rod-like bodies, more or less closely and irregularly 

 connected together : here and there will be seen highly re- 

 fractive pyrenoids attached to the chromatophores : these are 

 clearly to be distinguished by their dusky purple staining on 

 treatment with iodine solution. 



3. A single nucleus which is, however, difficult to recognize 

 in well-nourished cells. 



4. A large central vacuole. 



II. An examination of fresh filaments may result in the ob- 

 servation of the reproductive organs, and numerous specimens 

 should be looked over with the object of finding them. Thus 

 the reproduction by swarm-spores may be seen, especially in 

 the morning : without the cell having undergone any change of 

 form the cell-wall ruptures by a transverse split, and the proto- 

 plasmic body, having previously contracted, escapes through 

 the slit as a motile pear-shaped, primordial cell, the anterior 

 end of which is surrounded by a fringe of cilia. After a motile 

 period these attach themselves by the anterior end to some firm 

 body, and, forming a cell-wall, develop into new filaments. 

 Note young plants in early stages of germination : they may be 

 found in numbers attached to submerged plants or stones in 

 waters where (Edogonium grows. 



III. There is some variety in the details of development of 

 the sexual organs in different species of (Edogonium : some 

 species are monoecious, others dioecious. 



