MISCELLANEOUS: EXPERIMENTAL TERATOSIS 619 



dance on other green plants. On the upper surface of the leaves 

 I have not found any stomata and on the lower surface the aver- 

 age is only about 20 per square millimeter, but in this respect it 

 is not different from a half dozen other begonias I have examined. 

 32. When new phenomena appear our first thought is to 

 inquire whether there are any old and well-known phenomena 

 which can be linked up with the new appearances and thus serve 

 to explain them and also whether there are any other unsolved 

 problems on which they themselves will serve to throw light- 

 In this case one naturally thinks of root-pruning or bruising, 

 sometimes used to throw sterile fruit trees into bearing; of the 

 development of young plants from the leaf margins of Bryo- 

 phyllum calycinum, which also occurs, so far as I have observed, 

 only when the water-supply is interfered with, i.e., when the 

 leaves are severed or partly severed from the stem or when w T ater 

 is withheld from the roots, or is drawn away from lower leaves to 

 more active upper leaves, but here, while the stimulus appears 

 to be the same, we have to do not with pathological or semi- 

 pathological phenomena, or with regeneration, as I understand 

 the term, but only with the growth of preformed dormant buds 

 located in unusual places but otherwise normal; of prolepsis and 

 prolification in peach trees attacked by peach yellows and peach 

 rosette, where I have satisfied myself that there is premature 

 death of a great many feeding roots, so that loss of water might 

 exceed the intake, although the cause of this root-injury remains 

 to be determined; of regeneration in general in plants and 

 animals where the response is directly from the wounded surface 

 or the cells in its vicinity, as it is in this begonia when young 

 leaves are wounded; of crown-gall embryomas, where the shock 

 which causes the development of roots and shoots in the tumors 

 is connected with the presence in the tissues of the products of 

 Bacterium tumefaciens and the growth of the tumors in the 

 vicinity of totipotent cells, which are also set growing; of intu- 



and occupies deeper parts of the leaf . From a stained serial section. For a 

 much earlier stage see Fig. 453 at X. X 55 circa. 



B. Cross-section of an internode showing superficial origin of the proliferous 

 shoot. The phloem-xylem is a long distance below the part here shown and no 

 vessels extended into it. Section photographed unstained in water. X 75 circa. 



