MYXOPHYCOPHYTA 293 



pericentral cells are formed which are arranged approximately 

 longitudinally. In young plants the sheath is continuous at the tip, 

 but when growth is rapid the end is burst and also when hormo- 

 gones are produced and extruded. The heterocysts in this genus 

 are commonly lateral being formed by tangential division of a cell. 

 The filaments are often aggregated to form a macroscopic yellow- 

 green gelatinous mass. The species are most common where there 

 is continual dripping water. 



REFERENCES 



Heterocyst 



Fogg, G. E. (1949). Ann. Bot. Lond., N.S., Jj, 241. 



(1951). Ann. Bot. Lond.^ N.S. 15, 23. 



Fritsch, F. E. (195 1). Proc. Linn. Soc. Lond.^ 162 (2), p. 174. 

 General 



Fritsch, F. E. (1945)- The Structure and Reproduction of the Algae, Vol. 

 II5 pp. 768-79. Camb. Univ. Press. 



Systematic 

 Geitler, L. (1932). 'Cyanophyceen' in Rabenhorst's Kryptogamen 



Flora, Vol. 14. Leipzig. 

 Tilden, J. (1910). Minnesota Algae, Minneapolis. 



