Other containers are not planted with the tree, e.g., Styroblock, Superblock, Copperblock, and Miniblock container systems, produce Styroplug seedlings with roots in a cohesive plug of growing medium. The plug cavities vary in volume by various combinations of top diameter and depth, from 39 to 3260 mL, but those most commonly used, at least in British Columbia, are in the range 39 mL to 133 mL (Van Eerden and Gates 1990). The BC-CFS Styroblock plug, developed in 1969/70, has become the dominant stock type for interior spruce in British Columbia (Van Eerden and Gates 1990, Coates et al. 1994). Plug sizes are indicated by a 3-figure designation, the 1st figure of which gives the top diameter and the other 2 figures the depth of the plug cavity, both dimensions approximations in centimetres. The demand for larger plugs has been increasing strongly (Table 6.24; Coates et al. 1994). Stock raised in some sizes of plug can vary in age class. In British Columbia, for example, PSB 415 and PSB 313 plugs are raised as 1+0 or 2+0. PSB 615 plugs are seldom raised other than as 2+0.