And one more response, this one on naming of generations when it comes to cultures on agar:
The Stamets “P” Value System
The Stamets “P” value system is simply an arithmetic scale I have devised for measuring the expansion of mycelium through successive inoculations from one 100 x 15-mm petri dish to the next. […] The Stamets “P” Value (SPV) benefits cultivators by indicating how close to the origin their culture is at any point in time by simply recording the number of petri dishes the mycelium has grown through. When a culture has been isolated from contaminants, usually in one or two transfers, the first pure culture is designated as P1. When the mycelium has filled that dish, the next dish to receive the mycelium is called P2. Each culture is labeled with the date, species, collection number, strain code, “P” Value, and medium (if necessary). Thus, a typical example from one of my culture dishes reads:
The date 2/12 refers to the time the medium was inoculated. Spawn created from such young cultures, in contrast to one grown out 100 times as far, produces more mushrooms. The “P” value system is essentially a metric ruler for measuring relative numbers of cell divisions from the culture’s birth. I have strains in my possession, from which I regularly regenerate cultures, that are 10 years old, and kept at a P2 or P3.
For purposes of commercial production, I try to maintain cell lines within P10, this is, within ten successive transfers to medium-filled petri dishes.
Growing Gourmet and Medicinal Mushrooms, 3rd edition. Page 99 - 100.
And here he mentions what my mentor taught me:
The slowing of mycelium may also be partly due to media specificity, i.e., the agar formula selectively influences the type of mycelial growth. To ameliorate degenerative effects, the addition of extracted end-substrates (sawdust, straw, etc.) favors the normal development of mycelium. The introduction of end-substrate acquaints the mushroom mycelium with its destined fruiting habitat, challenging the mycelium and selectively activating its enzymatic systems. This familiarity with the end-substrate greatly improves performance later on. Parent cells retain a “genetic memory” passed downstream through the mycelial networks. Mycelia grown in this fashion are far better prepared than mycelia not exposed to such cultural conditions. Not only is the speed of colonization accelerated, but also the time to fruiting is shortened.
Growing Gourmet and Medicinal Mushrooms, 3rd edition. Page 100.