Aristotle's biology vitality; and in a word, the whole genus of plants, whilst it is devoid of life as compared with an animal, is endowed with life as com- pared with other corporeal entities. Indeed, as we first remarked, there is observed in plants a continuous scale of ascent towards the animal. So in the sea, there are certain objects concern- ing which one would be at a loss to determine whether they be animal or vegetable. For in- stance, certain of these objects [e.g. sponges] are fairly rooted, and in several cases perish if detached. . . . Indeed, broadly speaking, the entire genus of testaceans has a resemblance to vegetables, if they be contrasted with such animals as are capable of progression. " In regard to sensibility, some animals give no indication whatsoever of it, whilst others indicate it but indistinctly. Further, the sub- stance of some of these intermediate creatures is fleshlike ... but the sponge is in every respect like a vegetable. And so throughout the entire animal scale there is a graduated differentiation in amount of vitality and in capacity for motion. " A similar statement holds good with regard to habits of life. Thus of plants that spring from seed the one function seems to be the
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