§2] 



GEOTKOPISM 



399 



sentatives of this group show themselves, however, markedly 

 xesponsive. 



The first observations upon geotropism in hydroids seem to 

 have been made by Loeb ('91% pp. 27, 28). He says : "When 

 a stolon was formed at the cut end of a vertical stem (of Ag- 

 laophenia) it grew (in case it did not come in contact with a 

 solid body) first a short distance horizontally, and then down- 

 wards. In horizontal stems the stolon grew directly down- 



no 



109 



Tig. 109. — Positive geotropism of regenerated stolons {Wi, W-^ and negative geotro- 

 pism ol regenerated hydranths of Aglaoplienia pluma. The original piece of the 

 stem is included between 6 and c. This piece was placed vertically, right end up, 

 in the aquarium. At the cut end, 6, the stolon (W{) has arisen, but has soon begun 

 to grow downwards. It has produced a vertical hydranth at s. Wn, an adventi- 

 tious stolon. (From Loee, '91'.) 



Fig. 110. — Two bits of regenerating stems of Antennularia antennina. The one at 

 the left is in the normal position ; that at the right is inverted. From both, new 

 hydranths (S) have developed at the upper end, and new stolons {W) at the lower 

 end. (From Loeb, '92.) 



