Low-priced stock that sells at less than $1.00 per share. Often highly-speculative and volatile, such as start-up mining companies. While, in general, penny stock are considered high-risk securities, some penny stock mature into less-speculative investments. All penny stock are traded over-the-counter.
In its natural form, cork is also a very good fire retardant, although cork dust is actually extremely flammable (because here the cell structure has been broken down). Impermeable: Cork has a magic chemical in its cell membrane that makes it completely impermeable to liquids and gases.
Mature cork cells are dead; their cell walls contain suberine, a fatty substance that repels water. The layer of cork provides protection against desiccation, but it also isolates tissues in the inner parts of the stem or trunk so thoroughly that exchange of gas with the outer world is impeded.