A system for directing water, nutrients and air to the root system of a plant includes an elongated, hollow housing having a wall member that permits water and air to be transmitted therethrough and which defines an internal cavity with an open top and an open bottom. The displays are arranged in a manner such that the data can be easily analyzed and readily acted upon. The variation characteristic altering element alters a characteristic of the air-fuel variation depending on an stored CO quantity correlative value which correlates with a quantity of CO stored by the CO storage component. The electrode is provided around of the opening of the through-hole.