A rolling stone, they say, gathers no moss. But it appears for growing numbers of entrepreneurs, gathering moss is becoming quite popular, and this has botanists concerned.   According to a recent article in the New York Times, moss can fetch about $5 for a four ounce bag — and this has helped spawn the gathering of perhaps 40 million pounds of the plant from our forests, much of it illegally.  Moss is important, biologists note, to healthy ecosystems — as they are home to some 300 species of insects and provide nesting for the endangered marbled murrelet.  Since the regeneration of moss can sometimes take over 100 years, here’s hoping wildlife officials can find a blanket solution to this growing moss problem.