Experiments were carried out on the conditions favouring strand formation in the mycelium of Serpula lacrimans. The mechanism of strand production proposed by Garrett and Butler (1960) was taken as a working hypothesis.
Colonies of the fungus were grown on a liquid medium of a nutrient composition found previously to induce stranding. In one set of cultures this medium was renewed daily by slow perfusion of fresh medium through the culture vessels, continued over a 6-week period. In a parallel set of cultures the medium remained static and was not renewed over the same period. Strands formed only in these static cultures and not in the perfused ones. When the fungus was grown from a nutrient-rich food base over media at a range of lower concentrations it was found that there was an optimal lower concentration for strand formation. Another state of nutrient supply that favoured the formation of strands occurred when mycelium growing out from a food base over a non-nutrient medium encountered and began to colonize a fresh food base. This observation, first made on Helicobasidium purpureum by Valder (1958), was repeated using Serpula lacrimans and it was also shown by using 14C-labelled glucose that carbon was transported between old and new food bases. Further experiments using 14C as a tracer showed that there was a loss of substances containing carbon from intact hyphae and from strand-forming mycelium.
The significance of these results is discussed, and it is suggested that to Garrett's original hypothesis might be added the proposition that nutrient leakage from older hyphae is part of the process of strand induction.