Great Lakes lettuce, adapted to culture under a range of environmental conditions, normally produces a medium-large, globular, semi-exposed head. In some plantings, however, a percentage of the plant population develops conical-shaped heads, with the wrapper leaves or head leaves in a spiral-like fold. Market-stage plants of this type are generally referred to as spiraled heads. The shipper and retailer prefer a slightly oblate head with broad, flat butt, which can be packed evenly and firmly.

The above progress report is based on Research Project No. 1175.