a dendrobium orchid in a garden in Bangkok, Thailand; Dendrobium are very popular orchids because of their easy growth on trees or any support, low price and what is less known as detection of pollution; a dendrobium branch will last at least 4 weeks with clean air conditions; the shorter the blooming period, the higher the ambiant pollution; it is very helpfull in Thai houses where it detects Deadly carbon monoxyde leakage better than any sophisticated instrument! premature wilting of a dendrobium flower indicates CO leakage;