3 2 RE GENERA TION 



Loeb, if the pieces are suspended obliquely. In a piece of this sort, 

 it is found that new stems arise along the upper surface of the old 

 stem, and roots from the lower surface as well as from the lower 

 cut-end (Fig. 14, D, E). If a piece of the stem is placed horizontally 

 on the bottom of an aquarium, the branches that come off from the 

 under surface of the stem begin to grow downwards at their ends, 

 and where they come in contact with a solid body they fasten them- 

 selves to it, thus showing that they are true roots (Fig. 14, F). One 

 or more stems may arise from the upper side of the main stem. 

 These stems grow vertically upwards, and produce lateral branches. 

 Only in one case did a new stem, or stem-like structure, arise from 

 one of the vertical branches, as shown to the left in Fig. 14, F. 



Losb found it also possible to change the character of the growth 

 of the apex of the normal stem and to transform it into a root. A long 

 piece of the hydroid was cut off and suspended vertically with the 

 basal end upwards. From the upper end a new stem began to grow, 

 and then the entire piece was reversed, so that the new stem pointed 

 downwards. Under these circumstances the young stem did not 

 bend around and begin to grow upwards, as a young plant might 

 have done, but it ceased to grow as a stem, and at its apex one or 

 more roots developed. Loeb concludes : " I cannot imagine by 

 what means the place of the formation of organs in antennularia 

 is determined in connection with the orientation of the animal except 

 by means of gravity." 



The response of antennularia to the action of gravity is, I think, 

 conclusively demonstrated by Loeb's results, but that the phenomenon 

 may be complicated by other factors is shown, I think, by the follow- 

 ing experiments. Driesch found that if pieces of antennularia are 

 cut off and placed between horizontal plates, so that both ends are 

 free, roots are produced by the basal end. 1 If the basal end with its 

 new roots is cut off, new roots may appear, but sometimes a thin 

 stem also. If the end is again cut off, a larger stem, and also one or 

 two roots, may appear, and if the operation is repeated again only 

 a stem is formed. The factor that brings about this change is not 

 shown by the experiment. The piece had been kept in a horizontal 

 position throughout the whole time. The apical end died in most 

 cases without producing roots, but it is not stated whether or not 

 roots appear on the stem between the plates of glass. If they 

 develop they may affect the result, as certain experiments that I have 

 made seem to show. 



In my experiments, made at a different time of year from that at 



1 Driesch does not give in his paper ('99) the position of the hydroids, or the method of 

 the experiment, but I can supply the details given above from a personal communication 

 from Driesch. 



