Cores must be taken at the stolon attachment site and must be conical or semi-spherical in shape, approximately 1 cm in diameter at the top and 1 cm deep. Each core should weigh between 0.5 – 1.0 g, and include as much of the vascular ring radiating from the stolon attachment as possible.

The above information was found at the following website:
http://www.inspection.gc.ca/english/plaveg/protect/dir/d-97-12e.shtml