are filled with rooting medium and planted with the tree (Tinus and McDonald 1979). Also planted with the tree are other containers that are not filled with rooting medium, but in which the container is a molded block of growing medium, as with Polyloam, Tree Start, and BR-8 Blocks. Designs of containers for raising planting stock have been many and various. Containerized white spruce stock is now the norm. Most containers are tube-like; both diameter and volume affect white spruce growth (Hocking and Mitchell 1975, Carlson and Endean 1976). White spruce grown in a container having a 1:1 height:diameter produced significantly greater dry weight than those in containers of 3:1 and 6:1 height:diameter configurations. Total dry weight and shoot length increased with increasing container volume. The larger the bag the fewer deployed per unit area. However, the biological advantage of size has been enough to influence a pronounced swing towards larger containers in British Columbia (Coates et al. 1994). The number of PSB211 (2 cm top diameter, 11 cm long) styroblock plugs ordered in British Columbia decreased from 14,246,000 in 1981 to zero in 1990, while orders for PSB415 (4 cm top diameter, 15 cm long) styroblock plugs increased in the same period from 257 000 to 41 008 000, although large stock is more expensive than small to raise, distribute, and plant. 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