615 plugs are seldom raised other than as 2+0. Initially, the intention was to leave the plugs in situ in the Styroblocks until immediately before planting. But this led to logistic problems and reduced the efficiency of planting operations. Studies to compare the performance of extracted, packaged stock versus in situ stock seem not to have been carried out, but packaged stock has performed well and given no indication of distress. Forestry Field storage As advocated by Coates et al. (1994), thawed planting stock taken to the field should optimally be kept cool at 1 °C to 2 °C in relative humidities over 90% (Ronco 1972a). For a few days, storage temperatures around 4.5 °C and humidities about 50% can be tolerated. Binder and Fielder (1988) recommended that boxed seedlings retrieved from cold storage should not be exposed to temperatures above 10 °C. Refrigerator vans commonly used for transportation and on-site storage normally ‘maintain seedlings at 2 °C to 4 °C (Mitchell et al. 1980). Ronco (1972a, b) cautioned against using dry ice (solid carbon dioxide) to cool seedlings; he claimed that respiration and water transport in seedlings are disrupted by high concentrations of gaseous carbon dioxide. Coniferous planting stock is often held in frozen storage, mostly at −2 °C, for extended periods and then cool-stored (+2 °C) to thaw the root plug prior to outplanting. Thawing is necessary if frozen seedlings cannot be separated from one another and has been advocated by some in order to avoid possible loss of contact between plug and soil with shrinkage of the plug with melting of ice in the plug. Physiological activity is also greater under cool rather than frozen storage, but seedlings of interior spruce and Engelmann spruce that were planted while still frozen had only brief and transient physiological effects, including xylem water potential, (Camm et al. 1995, Silem and Guy 1998). After 1 growing season, growth parameters did not differ between seedlings planted frozen and those planted thawed. Studies of storage and planting practices have generally focussed on the effects of duration of frozen storage and the effects of subsequent cool storage (e.g., Ritchie et al. 1985, Chomba et al. 1993, Harper and Camm 1993). Reviews of colds storage techniques have paid little attention to the thawing process (Camm et al. 1994), or have merely noted that the rate of thawing is unlikely to cause damage (McKay 1997). Kooistra