ABSTRACT

Plants, like any other organisms, are able to exist as highly organized systems open to the environment. Plant life can only be maintained when energy and matter are taken up from the surrounding milieu, incorporated into the body, and eventually dissipated or released as heat or waste. Taking up substances from the environment and transporting them within the body are both characteristic traits and basic, indispensable prerequisites of plant life. But the flow of matter and energy between the environment and the interior must be under physiological control. Homoeostasis, the control of the internal milieuof theorganism, is another indispensablepropertyof life,which requires that the organism gain control over the quality and quantity of material exchange with the environment and over the temporal pattern of exchange.