194 



Regeneration 



in stems of Bryophyllum placed horizontally the roots 

 usually come out from the lower end of the callus. 

 Such phenomena are not often found in animals but 

 they exist here too as the following observation shows. 

 If we cut a piece a b (Fig. 37), from the stem ss oi 



FIG. 37 



Antennularia antennina (Fig. 38), a hydroid, and put it 

 into the water in a horizontal position, new stems cd 

 (Fig. 37) may arise on its upper side. The small branches 

 on the under side of the old stem a b begin suddenly to 

 grow vertically downward. 1 In appearance and func- 

 tion these downward-growing elements are entirely 

 different from the branches of the normal Antennularia; 

 they are roots. In order to understand better the 

 transformation which thus occurs in these branches, it 

 may be stated that under normal conditions they have 



1 Loeb, J. f Untersuchungen zur physiologischen Morphologic def 

 Tiere. II. Organbildung und Wachsthum. Wurzburg, 1892. 



