The Fungus‐alga Association in the Lecanoraceae: An Ultrastructural Study*

Summary Electron micrographs of four lichen species of the Lecanoraceae were examined. The contact between the symbionts ranges from active penetration of the algal cell wall by fungal haustoria in a supposedly primitive growth‐form, through intermediate stages, to a kind of hyphal entrapment in an advanced form. Penetration beyond the plasma membrane of intact algal cells has not been observed. Whereas penetrations may occur in all the algal cells composing the algal layer of the primitive thallus, in the more advanced growth‐forms, only those cells which have reached a certain stage of their life cycle are attacked.