164 



Regeneration 



more quickly than the formation of roots and shoots 

 in the notches of a completely isolated leaf. The stem 



FIG. 1 8 



FIG. 19 



FIG. 20 



acts therefore as a centre of suction for the flow of 

 substances from the leaf and this prevents or retards 

 the formation of roots and shoots in the notches. In 

 the isolated leaf of Bryophyllum calycinum no callus 

 formation takes place and hence no flow of the sap 



