Fig. 7.—Stentor cœruleus. A. Normal, fully expanded individual. A¹. Same contracted. Line a-a indicates where it was cut in two. B, C. Pieces after division. B¹, B², B³. Regeneration of three distal pieces (B) containing old peristome. C¹, C². Regeneration of two proximal or foot pieces (C).
A similar change takes place in pieces of unicellular animals, as best shown by cutting off pieces of stentor. If Stentor cœruleus is cut in two pieces, as indicated in [Fig. 7], each piece makes a new individual of half size, but of proportionate form. The old peristome remains on the anterior piece, but becomes reduced in size as the piece changes its shape, and although it may be at first too large for the length of the new piece, it ultimately reaches a size about proportionate to the rest of the animal. The posterior piece is at first too long for the size of the new peristome that is formed, but the latter becomes larger, until the characteristic form has been reached. The change in form of the stentor may take place in a few hours, and the result is brought about, not by the development of new protoplasm over the cut-end, but by a change of the old protoplasm into the new form. A similar experiment is shown in [Fig. 8], in which a stentor was cut into three pieces, each piece containing a part of the old nucleus.
Fig. 8.—After Gruber. Stentor cœruleus. A. Cut into three pieces. B. This row shows regeneration of anterior piece. C. This row shows regeneration of middle piece. D. This row shows regeneration of posterior piece.
REGENERATION IN PLANTS
In the higher plants the production of a new plant from a piece takes place in a different way from that by which in animals a new individual is formed. The piece does not complete itself at the cut-ends, nor does it change its form into that of a new plant, but the leaf-buds that are present on the piece begin to develop, especially those near the distal end of the piece, as shown in [Fig. 32], A, and roots appear near the basal end of the piece. The changes that take place in the piece are different from those taking place in animals, but as the principal difference is the development of the new part near the end, rather than over the end, and as in some cases the new part may even appear in new tissue that covers the end, and, further, since the process seems to include many factors that appear also in animals, we are justified, I think, in including this process in plants under the general term regeneration.
