The best opinion now is, that there are multitudinous forms which are not sufficiently differentiated to be distinctively either plant or animal, while, as respects ordinary plants and animals, the difficulty of laying down a definition has become far greater than ever before.
Asa GrayThis view, as a rounded whole and in all its essential elements, has very recently disappeared from science. It died a royal death with Agassiz.
Asa GrayWe have spoken of beings so low in the scale that the individuals throughout their whole existence are not sufficiently specialized to be distinctively plant or animal: yet these are definite life in simpler shape.
Asa Gray