422 TEXTBOOK OF BOTANY 



the tip. Some plants, such as apple, which fail to propagate from stem 

 cuttings taken from the crown of the tree, propagate readily from root 

 cuttings. Moreover, sprouts from the roots of apple may be used as stem 

 cuttings, in contrast to branches from the crown. 



Leaf cuttings. For many years floriculturists have used the leaves of 

 certain species of plants as vegetative propagules. Among those most 

 frequently used are the leaves of the African violet, begonia, pepperomia, 

 sedum, echeveria, lily (bulb scales), bryophyllum, bowstring hemp, and 

 kalanchoe (Fig. 194). 



Vegetati\'e multiplication fails completely in some leaves, and is in- 

 complete in others, because adventitious stem and root primordia do 

 not develop in them. When the lower end of the petiole of a leaf of 

 English ivy is inserted in soil, roots develop from the petiole and the 

 blade enlarges and lives for many years, but no shoots develop. If a leaf 

 of sweet potato is treated in the same manner, roots develop and then 

 aerial shoots develop from the roots. 



One investigator, after testing the probable use of leaves of more than 

 600 species of plants as vegetative propagules, reported the following 

 results : no vegetative multiplication in 32 per cent of the species, growth 

 of roots but no shoots in 42 per cent, growth of shoots but no roots in 2 

 per cent, and growth of both roots and shoots in 24 per cent. 



The behavior of vegetative propagules is much more variable than that 

 of seeds. Only the merest outline of information about them can be 

 given in a single chapter. Detailed information desired about specific 

 varieties and methods may be found in encyclopedias of horticulture 

 and in special research papers. 



REFERENCES 



Bailey, L. H. Hortus. The Macmillan Company. 1935. 



Chandler, W. H. Fruit Growing. Houghton Mifflin Company. 1925. 



Denny, F. E., P. W. Zimmerman, and A. E. Hitchcock. Contributions from 

 the Boijce Thompson Institute. 1929-40. 



Priestley, J. H., and C. F. Swingle. Vegetative propagation from the stand- 

 point of plant anatomy. U. S. D. A. Tech. Bull. No. 151. 1929. 



Salisbury, E. J. The Living Garden. The Macmillan Company. 1936. 



Stoutemyer, V. T. Regeneration in various types of apple wood. Iowa Agr. 

 Exp. Sta. Research Bull. 220. 1937. 



Yerkes, G. E. Propagation of trees and shrubs. U. S. D. A. Farmers Bull. 

 1567. 1929. 



Zimmerman, P. W. Responses of plants to hormonelike substances. Ohio Jour. 

 Sci. 37:333-348. 1937. 



