LEAVES 



637 



which in Cystopteris drop off and germinate in the ground. In Asplenium they 

 may germinate and grow to considerable size while attached to the leaf (fig. 932), later 

 falling to the ground where development is continued. When the leaf tip of the 

 walking fern (Camptosorus) comes in contact with the ground, a bud forms from 

 the terminal cells, later developing into a plant. In Adiantum Edgeworthii the 

 apical cell of a leaf may develop directly into a stem. In Camptosorus some ex- 

 ternal factor (perhaps moisture) stimulates vegetative reproduction, but the stimu- 



FIG. 933. The 

 upper portion of a 

 plant of Bryophyl- 

 lum calycinum, 

 showing new plants 

 (p) developing from 

 buds that originate in the 

 leaf sinuses; note also the adventi- 

 tious roots (r) which develop at the 

 stem nodes, appearing from all sides where 

 the stem is vertical or ascending, but from the 

 under side only where the stem is horizontal. 



FIG. 934. Vegetative re- 

 production in Sansevieria arti- 

 ficially induced through the use 

 of a leaf cutting; a bud and a 

 copious growth of roots origi- 

 nate at the basal part of the cut- 

 ting when placed in moist soil. 



lating factor in Asplenium and Cystopteris is unknown. The leaves as well as 

 various other organs of mosses exhibit vegetative reproduction (see p. 807). 



Seed plants. In the seed plants natural leaf reproduction is a rare phenomenon. 

 In Tolmiea and in Cardamine pratensis new plants may appear on the leaf blade 

 near the petiole, and in Bryophyllum at the sinuses along the leaf margin (fig. 933). 

 Moisture appears to facilitate development in Bryophyllum, but the more vigorous 

 development of new plants on a severed leaf, even in dry air, seems to suggest a 

 release from some inhibitory factor residing in the plant (see p. 749). In many 

 plants (as Peperomia and Begonia) a bud soon forms on a severed leaf placed in the 

 soil, later growing into a plant ; in Sansevieria, leaves may be cut into a number of 

 pieces, each of which will produce a bud if placed in the soil (fig. 934). A number 

 of species are propagated in this manner by florists, and it has been shown that 



