Regeneration 249 



of such conversion and studied a particularly good example of it in 

 Torenia asiatica. He believed that increased transpiration is the cause of 

 the change. Simon (1929) found essentially the same thing in Begonia 

 and noted that the bundles from the young roots induced new vascular 

 tissue only in that part of the petiole just below them, suggesting the 

 polar distribution of a hormone. Similar results were obtained by Doyle 

 (1915) through grafting buds onto the petioles of rooted leaves. 



In leaf cuttings, adventitious structures are formed predominantly at 

 the leaf base. Hagemann (1931), in an extensive survey of the regener- 

 ative ability of leaves, investigated 1,204 species of gymnosperms, dicoty- 



Fig. 9-7. Petals of Epilobium angustifolium which produced roots when cultured on 

 nutrient agar. ( From La Rue. ) 



ledons, and monocotyledons. He found that some of these showed no 

 restoration, a very few formed shoots or both roots and shoots, and the 

 largest proportion roots only. Schwarz ( 1933 ) examined many other spe- 

 cies. The location of the regenerated structures is determined mainly by 

 the anatomy of the leaf. It is noteworthy that in a number of species, pre- 

 dominantly though not always succulents, restoration and vegetative 

 reproduction occur in other parts of the leaf than the base, as in species 

 of Drosera, Achimenes, Begonia, Torenia, and the Crassulaceae. In Utric- 

 ularia Goebel (1908) found adventive shoots formed by the leaf tips. 



Restoration of organs may also occur from isolated cotyledons. Kiister 

 ( 1903fo ) obtained both roots and shoots from cotyledons of Cucumis and 



