l6 HEREDITY AND EVOLUTION IN PLANTS 



through long geological ages, foliage-leaves have in gen- 

 eral originated by the sterilization of spore-bearing organs . 

 9. Vegetative Multiplication. — In addition to repro- 

 duction by spores, ferns may also be propagated vege- 

 tatively in at least four ways. By one of these methods, 

 the rhizome is cut into several pieces, and from every 

 piece that contains a bud a new plant will develop. By 



Fig. i8. — ^A Boston fern (Nephrolepis), reproducing vegetatively by- 

 means of runners or stolons. The parent plant is in the round pot. 

 (After R. C. Benedict.) 



the second method, the plant is progagated by means of 

 bulbils, which occur on the foliage-leaves of several species. 

 In the fern Tectoria cicutaria, bulbils occur on both the 

 upper and under sides of the leaf (Fig. i6). These bulbils 

 fall to the ground, and under suitable conditions of light, 

 moisture, and temperature give rise to new fern-plants. 

 One of the ferns native to the eastern United States 

 {Cystopteris bulbifera) received its specific name from the 



