ORGANIZATION AND GROWTH 



195 



essential point is again this, that the place of the new growth 

 is determined by the orientation of the stem toward the cen- 

 ter of the earth, inasmuch as stems arise only from the upper 

 surface, the roots only from the lower surface, of the element. 

 That a new stem may arise from the upper surface of any 



FIG. 45 



element of a stem which is put obliquely is evidenced by the 

 fact that such stems arise at times from the upper surface of 

 the lowest elements of the animal. Such a case is shown in 

 Fig. 45. The stem of an Antennularian was bent so that 

 the two ends were directed obliquely downward. New stems, 



$ n $ 2 , $ 3 , S 4 , $ 5 , have formed upon 

 of different elements of the old stem. 



the upper surfaces 

 Si has grown from 



