254 The Phenomena of Morphogenesis 



The most familiar examples of reproductive regeneration are provided 

 by members of the Crassulaceae. In Kalanchoe pinnatum ( Bryophyllum 

 calycinum), plantlets develop from the marginal notches of the fleshy 

 leaves. This may sometimes take place while the leaf is attached to the 

 plant but is more common after it has fallen to the ground. In each 

 notch is a preformed foliar embryo (Fig. 9-12), long ago described by 

 Berge (1877) and more recently by Yarbrough (1932) and Naylor 

 ( 1932 ) . This is more than a mass of meristematic cells, for it has already 

 taken the first steps toward organization of a plantlet and shows the 

 minute beginnings of root, stem, and leaf. In other species the degree 



Fig. 9-11. Development of an adventitious bud from cells of the leaf epidermis of 

 Saintpaulia. ( From Naylor and Johnson. ) 



of differentiation of the foliar embryos varies (Stoudt, 1938). In K. 

 daigremontana and K. tubiflora the plantlets attain appreciable size be- 

 fore the parent leaf has reached maturity. In K. rotundifolia there is a 

 residual meristem on the axial surface of the petiole which develops a bud, 

 but root primordia do not become differentiated until after the leaf has 

 fallen from the plant. 



The factors that induce the foliar embryos to develop into plantlets 

 have been actively discussed. Loeb (1920), who made an extensive study 

 of regeneration in this genus, believed that a hormonal mechanism in- 

 hibited their growth as long as the leaf was attached to the plant. Reed 

 (1923) attributed their behavior to the metabolic condition of the leaf 

 and showed that they tend to grow if the lamina loses vigor. Ossenbeck 



