Influence of arbuscular mycorrhizal (AM) fungi (Glomus intraradices) and host plant (barley) on haustorium initiation and differentiation, and survival of transplanted Pedicularis tricolor in expt 2. (A) Total number of haustoria per gram of dry root. (B) Presumably functional haustoria (PFH) per gram of dry root. (C) PFH as a percentage of total haustoria. (D) Percentage survival of P. tricolor. Data are presented as the mean ± s.e. of six replicate pots. Different letters indicate a statistically significant difference at the P < 0·05 level. H–My + , no host plant of P. tricolor but with AM inoculation; H–My–, no host plant and without AM inoculation; H + My + , presence of a host plant and with AM inoculation; H + My–, presence of a host plant but without AM inoculation.