Regeneration 255 



( 1927 ) regards the mechanical or physiological conduction between the 

 leaf and the growing points of stem and root as important factors in 

 inducing their development. Mehrlich ( 1931 ) exposed plants to a wide 

 range of environmental factors in an attempt to solve the problem. In the 

 activity of certain enzymes and in the relative amounts of carbohydrates, 

 he noticed a difference between leaves in which the foliar embryos grew 

 out and those where they did not. Varietal differences were also evi- 

 dent. Gotz (1953) finds that plantlets grow out readily in long days 

 but that short days tend to inhibit them. They are accelerated if the 



Fig. 9-12. Section through a notch on 

 the leaf of Kalanchoe, showing a pre- 

 formed "foliar embryo" with two leaf 

 primordia below and a root primor- 

 dium above, buried in the tissue. 

 (From E. E. Naylor.) 



vessels between lamina and petiole are cut or if auxin levels are low 

 (Vardar and Acarer, 1957). 



Other Crassulaceae differ in some respects from Kalanchoe. In Byrnesia 

 weinbergii, Stoudt (1934) found that the foliar meristem from which a 

 plantlet comes is at the base of the blade, not the margin. It is quite 

 undifferentiated and will not develop until the leaf is removed from the 

 plant. In Sedum (Yarbrough, 1936c) there are no preformed meristems 

 at all, but these arise after the leaf is detached. 



In Crassula multicava (McVeigh, 1938) a still different condition oc- 

 curs and one reminiscent of Begonia and Saintpaulia, for here, after a 

 leaf has been kept for a time in a moist chamber, plantlets begin to de- 

 velop. Entire plants— not the shoot alone, as in many other cases— have 



