The prothallia of certain ferns are said by Goebel to regenerate if cut in two; at least this is true for the part that contains the vegetative point. In a piece without the growing point, the cells are very little specialized, and the piece may remain alive; yet it is incapable of producing a new growing point. Comparing this result with the power of regeneration possessed by lower animals, Goebel states[34] that since in a plant new organs may arise without the typical form of the plant being produced, “therefore, the completion of a leaf, for instance, that has been injured, would _be of no use_ to the plant, while in animals that do not have a vegetative point, the loss of an organ is a permanent disadvantage in case the organ removed cannot be regenerated.” The “explanation” of the difference in the two cases is supposed, apparently, by Goebel, to depend on the usefulness, or non-usefulness, of the regenerative act! Brefeld has described several cases of regeneration in moulds. There is produced from the zygospore of _Mucor mucedo_ a germinating tube that forms at its end a single sporangium. If the tube is destroyed or injured, a second one is formed from the zygospore, and if this is injured a third time, a new tube is produced. Each time the sporangium is smaller than in the preceding case. If the spore-bearing stalk of _Coprinus stercorarius_ is cut off, the end grows out and produces a new sporangium. If pieces of the stem are cut off and placed in a nourishing medium, they produce from the ends a new mycelium, and from this new erect hyphæ may develop. In the former case, the cut-end regenerates the part removed in somewhat the same way that an animal regenerates at the cut-end; in the latter, there is a return to the mycelium stage, as in the piece of the moss that produces a new protonema. If the mycelium and the protonema are looked upon as an embryonic stage in the formation of the sexual form, there is a return in these cases to an embryonic form or mode of development. [Illustration: FIG. 36.--After Goebel. _Achimenes Haageana._ A leaf-cutting of a plant in flower. The new plant, regenerating at base of leaf-stalk, proceeded at once to produce a flower.]