Infected roots of clone VS1 and the cv. Huxley Giant were cut into segments and buried in 2 different field soils in envelopes of Tygan 131 netting at 2 depths and for varying periods of time, after which they were sampled for germination of the oospores. No germination was observed before burial or after 2, 5 or 10 weeks, but 2 germinating oospores were found in roots of Huxley Giant buried at 150 mm for 19 weeks at one site. Over 2000 oospores were checked in each sample but rates of germination were <1% after 20 weeks. The first indication of germination was the growth of germ tubes c. 25-40 mu m long with terminal swellings c. 20-30 mu m diam. which developed rapidly (usually in <30 min) into sporangia. These were typically pyriform, 20-30 mu m wide and 25-45 mu m long. Their contents were usually discharged within 1-2 h of the first appearance of the germ tube, as 8-16 motile zoospores. Oospores were not observed to germinate directly.