Fig. 3.

Effects of arbuscular mycorrhizal (AM) fungal inoculation on haustorium formation in Pedicularis tricolor. Haustoria are visible as swellings on roots, and some examples are shown with tailed arrows. (A) Presence of the host plant (barley) but without AM inoculation. The inset shows two haustoria (H) with a xylem bridge (XB) connecting a root of P. tricolor (PR) to a root of barley (BR). (B) Presence of the host plant (barley) with inoculation of Glomus intraradices. Note the lower density of haustoria compared with (A). The inset shows a haustorium with an XB connecting PR and BR. Colonization of barley by the AM fungus is also shown (AM).