326 Phillips on a Comparative Study of the 



nucleus radiate out toward the periphery of the cell, piercing 

 the chromatophore and cell wall, and project in the form of 

 the cilia which cause the movements of the trichomes. 



11. The finger-like processes upon the end cells of Oscil- 

 laria, and those surrounding the heterocysts and spores of 

 Cylindrospermum, are not parasitic, but definite organs of 

 the cell, having a motion of their own. They apparently 

 assist the trichomes to pass around obstacles. 



12. The protoplasts of the cells of filamentous Cyano- 

 phycese are all connected by fine protoplasmic threads which 

 pass through communicating pores in the walls. There is 

 usually one central pore, though other finer pores and 

 threads may be present. 



13. The heterocyst is a modified vegetative cell which 

 gradually fills with some substance, passed to it from the 

 other cells, through the pores for the protoplasmic threads 

 which connect it with the other cells of the trichome. This 

 substance finally fills the whole of the heterocyst. It gives 

 some of the reactions for chromatin and may be a modifica- 

 tion of that substance. The heterocyst of Cylindrospermum 

 will develop into a spore if it gets sufficient nutriment and 

 hereditary material passed into it from the other cells. 



14. Spores are formed in Oscillaria from groups of cells, 

 usually two, but it may be one, three or four. These fuse 

 by the absorption of their partition walls. The growth of 

 the spore is effected by substances passed into it from the 

 other cells. The spores of Cylindrospermum are formed 

 from a single cell which divides, the end cell becoming a 

 heterocyst and the second cell the spore. It also receives 

 substances from the other vegetative cells. 



15. The cell wall is composed of cellulose in its earlier 

 stages, but later becomes impregnated with or modified into 

 some substance akin to fungus cellulose. 



16. The cell wall is laid down as microsomata, in lamellae 

 on the inside of the cell wall. One such lamina is laid down 

 at each division. Thus every succeeding lamina from within 



