单选题 .    Even the newest gardener realizes that plants die without water. What is not so well known is that plants die equally decisively, though not so quickly, if they are overwatered.
    Beginners usually decide to play it safe and keep their potted (盆栽的) plants thoroughly wet. In consequence, death by drowning is one of the commonest disasters to befall (降临) the plants of a new horticulturist.
    Overwatered plants, unfortunately, do not give any such obvious signal. Unless the overwatered pot soil is given a considerable period without water, it will suddenly collapse in exactly the same way as the underwatered plant.1.  From the text we can infer that a horticulturist is a person engaged in ______.