The notion of a vegetable soul, in effect a level of complex organisation sufficient for life, was due to Aristotle: who suggested all living things had such a soul. Animals also had a second soul that animated them, enabling responses to sensation and locomotion. And humans were said to have a third, rational, soul, and so were more than just animals.
The vegetable soul, being in effect a reflection of a complex system, broke down at the death of the organism. The notion of souls as supernatural and/or immortal was not part of Aristotle's original concept.
