Hyphal wall growth in Neurospora crassa and Geotrichum candidum

Growth of the walls of hyphae of Neurospora crassa and Geotrichum candidum was studied using longitudinal and serial transverse sectioning methods. Rigidification of the hyphal wall below the extension zone did not appear to involve the gross formation of a secondary wall since the transition from extensible to non-extensible wall was not associated with an increase in thickness. However, behind the extension zone the walls leading hyphae of N. crassa increased in thickness until eventually they attained a thickness which was up to five times that of the tip wall. A hypothesis of hyphal wall growth is proposed.