THE VALIDITY OF THE MASS RELATION 



43 



in this and the next chapter but intend to show first that the same 

 laws or rules which determine regeneration in the leaf suffice, to 

 explain also regeneration in the stem. We will first prove that 

 the quantity of regeneration of a piece of stem exposed to light is 

 in direct proportion with the mass of the stem. 



Each node of the stem of Bryophyllum has 2 dormant buds 

 capable of growing into shoots. When a piece of defoliated stem 



In air 



ZP^ 



Fig. 35. — Two pieces of stem from the same plant, (1) apical, (2) basal. 

 Suspended in moist air, shoots formed only in the apical node, roots at the base. 

 The mass of shoots and roots is larger in the basal piece (2) which has the larger 

 Oct. 4 to Nov. 7. 



mass. 



is cut from a plant and suspended in moist air only the 2 buds of 

 the most apical node will grow into permanent shoots, while the 

 buds in all the nodes below will remain dormant (Fig. 35). Per- 

 manent roots will grow only at the base of each piece, though 

 transitorily air roots may begin to form in any node, but these 

 will dry out as soon as the basal roots are grovving. Figure 35 

 illustrates this polar character of regeneration in defoHated 

 pieces of stem suspended in moist air. When, however, a long 

 defoliated stem is cut into as many pieces as there are nodes 

 all the dormant nodal buds of the stem will grow out into shoots 



