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TEXTBOOK OF PLANT PHYSIOLOGY 



the formation of roots on the surface of the cut, just as in the 

 case of stem cuttings. However, because of the absence of buds, 

 no aerial organs are formed and such a leaf is incapable of develop- 

 ing into a new plant (Fig. 148) . It only increases in size somewhat, 

 and what is of particular interest will live much longer, even for 

 several years, while on the tree it might have lived at the most 

 one or two years. There are a few plants the leaves of which are 

 able to form adventitious buds when they are separated from the 

 mother plant. The best-known instance is the leaves of some of 

 the Begonias. If one of their leaves is placed on moist sand and 



Fig. 



148. — Rooted leaf of Aucuba 

 japonica (after Molisch). 



n 



Fig. 149. — The formation of shoots on 

 a Bryophyllum leaf (after Transeau). 



the larger veins are cut through, buds will appear on the points of 

 incision, which will later develop into new plants. This is a com- 

 mon gardener's method of propagating Begonias by means of 

 leaves. Some varieties of Cardamine, Bryophyllum (Fig. 149), 

 tomato, the hyacinths, and other plants have also the capacity 

 for producing buds from leaf cuttings. 



Cuttings which are separated from the plant even when very 

 small in size may restore all the other parts of a plant. This 

 is called "regeneration." Regenerational activity begins with the 

 formation of callus on the surface of the cut tissues. This results 

 from an increased division of cells adjoining the surface of the 



