330 



CAUSES OF VARIATION 



in Urbana, Illinois, eighteen inches or more in diameter. It 

 forked about six feet from the ground. A heavy storm split 

 one of the limbs away, when it was found that a dense net- 

 work of roots had formed in the moist soil that had collected 

 in the fork. 



FIG. 41. Regeneration in response to gravity in animal organisms : this creature 

 (Antennularia antennina) resembles plants in its habit of growth, being 

 attached ; it also resembles them in its response to gravity in regeneration. 

 After Morgan, from Loeb 



4. If the piece, be suspended apex down, the shoots will still 

 start from the apical end, bending upward, and roots will start 

 not only from the basal end, now uppermost, but they will start 

 from the whole length of the stem and bend downward, showing 

 that the force determining whether shoot or root shall be put out 



