The function of a heterocyst

Visited the university library in Turku and borrowed this book "Cyanophyta" from T.V. Desikachary, 1959. Still busy with the Cyanos after the Determination Course in Czech Republic...

It was very interesting to get some perspective in the study of Cyanos. Was reading the chapter Heterocysts and I realized that back in 1959 it was not yet clear what the function of heterocysts was. Different functions were suggested: store houses for food material, reproductive bodies, producing of gas vacuoles, secreting a growth stimulating substance.

The most surprising thing was that the germination of heterocysts was described by many researchers, even Geitler himself. I do wonder what they have really seen??

A bit earlier it was stated in the book that "certain blue-green algae have now been shown to be definitely able to fix atmospheric nitrogen". But in 1959 they had not yet combined these two thing, heterocysts and nitrogen fixation.

I wonder when and who actually did this?


Literature
Desikachary, T.V. (1959). Cyanophyta. pp. i-x, 1-686, 139 pls. New Delhi: Indian Council of Agricultural Research.