136 



PRINCIPLES OF PLANT-TERATOLOGY. 



vation, or as a result of mutilation, the instances can 

 be multiplied. In the enormous branching stem-like 

 leaves of the tomato (Solarium Lycop&rsicum) shoots 

 frequently appear in the " axils " of the petiolules of 

 the large leaflets (fig. 37). 



Gardeners make abundant use of the capacity 

 possessed by leaves of certain plants to form adven- 

 titious shoots in order to propagate such plants by 

 means of leaf-cuttings; for this purpose leaves of 

 Begonia, Gloxinia, Streptocarpus, and many others from 

 a great diversity of natural orders, are cut through 

 here and there in the region of the veins, and at the 

 points of incision new plants are formed when the 

 leaves are laid on moist soil. 



For other cases of regeneration induced by artificial 

 treatment the reader is referred to Groebel's book. 



But an instance cited by him may be mentioned in 

 which a youthful organ was shown capable of regene- 

 ration, but the mature organ quite incapable. Just as 

 the tadpole is able to regenerate amputated limbs, but 

 the frog cannot do so ; in the same way it was found 

 that the primordial leaves of Lycopodium inundatum 

 are able, but the mature leaves quite unable, to produce 

 adventitious shoots. 



From the morphological standpoint no more interest- 

 ing experiment is known than that recently described 

 by Doyle. " A sprout was grafted on a petiole of 

 Pelargonium zonal e var. meteor, all the other buds and 

 leaves being removed. After a short time the petioles 

 carried large shoots, completely functioning as stems, 

 while the qualities of a stem, viz., indefinitely active 

 cambium, the appearance of interfascicular cambium, 

 considerable secondary thickening, periclerm-formation, 

 were all taken on by the petiole:" This may be 

 regarded as a case of an adventitious shoot growing 

 on a leaf, but placed there by direct artificial means, 

 instead of arising in such a position naturally or as 

 the indirect result of an artificial environment. The 

 position of this shoot, terminal on the petiole, and 



