Plessner's distinction between plant and animal is both an enabling pathway towards his anthropology but also quite distinctive and worthy of consideration in itself. Contrary to the mainstream legacies of botany and zoology, but consistent with the logic he is developing, plants and animals for Plessner are a priori life-categories or modals of the organic based upon filling alternative organizational possibility spaces that follow from the dialectics of positionality and not in the first instance about the distinction between autotrophy and heterotrophy. Accordingly, certain heterotrophic species such as corals, hydroids, bryozoan and ascidians are classed by Plessner into the plant category. In broad terms, the plant-animal distinction is defined by the difference between "open" and "closed" positionalities, a distinction which has much to do with levels of mediation. One may think of this as two alternative basic strategies for achieving the aforementioned balance between assimilative and resistive moments immanent in any form of positionality. "A form is open if the organism in all of its expressions of life is immediately incorporated into its surroundings and constitutes a non-self-sufficient segment of the life cycle corresponding to it" (p. 203). An open form of positionality, we can say, doesn't require mediation by way of a posited center and the consequence of this is realized throughout the morphology, physiology and growth patterns of the plant. Morphologically this is manifested in the tendency of the organism to develop externally and expansively in a way that is directly turned toward its surroundings. It is characteristic of this kind of development that it does not have the need to form centers of any kind. The tissues responsible for mechanical solidarity, nutrition, and stimulus conduction are not anatomically or functionally concentrated in particular organs but rather permeate the organism from its outermost to it innermost layers. The absence of any central organs tying together or representing the whole body means that individuality of the individual plant does not itself appear as constitutive but rather as an external moment of its form associated with the singularity of the physical entity; in many cases the parts remain highly self-sufficient in relation to each other (graftings, cuttings). This led a great botanist to go so far as to call plants 'divididuals'. (pp. 203-204)