2] 



GEOTROPISM 



399 



sentatives of this group show themselves, however, markedly 

 responsive. 



The first observations upon geotropism in hydroids seem to 

 have been made by LOEB ('91 a , 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 



FIG. 109. Positive geotropism of regenerated stolons (W l9 TF 2 ) and negative geotro- 

 pism of regenerated hydranths of Aglaophenia pluma. The original piece of the 

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

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

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

 tious stolon. (From LOEB, '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.) 



