The dynamics of living matter . dynamicsofliving00loeb Year: 1906 218 DYNAMICS OF LIVING MATTER (Fig. 60). The parts which grow down (Fig. 59) have no polyps, but at- tach themselves like true roots to solid bodies. Thus the changed posi- tion of the stem alone, without any operation, suffices to transform the lateral branches, whose growth is limited, into roots with unlimited growth. The lateral branches on the upper side of the stem do not undergo such a transformation except in the immediate surroundings of the place where a new stem arises. It seems that the formation of a new stem also
The dynamics of living matter . dynamicsofliving00loeb Year: 1906 218 DYNAMICS OF LIVING MATTER (Fig. 60). The parts which grow down (Fig. 59) have no polyps, but at- tach themselves like true roots to solid bodies. Thus the changed posi- tion of the stem alone, without any operation, suffices to transform the lateral branches, whose growth is limited, into roots with unlimited growth. The lateral branches on the upper side of the stem do not undergo such a transformation except in the immediate surroundings of the place where a new stem arises. It seems that the formation of a new stem also causes an excessive growth of roots, possibly because the formation of new branches causes the removal of substances which naturally inhibit the formation of roots. If a piece from the stem be put vertically into the water with top downward, the upper- most point may continue to grow as a stem, while the lowest point may give rise to roots. In this case, therefore, a change in the orientation of organs has the effect of changing the character of organs. We have already mentioned the fact that in Eudendrium the formation or regeneration of polyps is only possible in the light. In many hydroids, contact with solid bodies seems to favor the formation of stolons, although such contact is not the only condition that brings about this result. Fig- ure 61 shows a piece of a stem of Pennaria, a hydroid, which was lying on the bottom of an FIG. 61. aquarium, and which formed stolons at both ends. In Margelis, another hydroid, I observed that, without any operation, the apical ends of the branches which were in contact with solid bodies continued to grow as roots, while those surrounded by sea water continued to grow as stems. FIG. 60.
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