63 



and the serrations were not formed again in this case, a certain return 

 to the original form of leaf occurred. This regenerative power of 

 immature leaves was found to be in contrast to the impotence of 

 damaged mature leaves. 



Comparative studies of observations on lower and higher animals 

 led BEIJERINCK to the proposing of six rules which should be valid for 

 plants also. These still deserve attention. Of these six we shall cite 

 only two: a) the regenerative power is greater, the younger the 

 organism and the tissues, and b) the lines along which regeneration 

 occurs coincide in many cases - - perhaps in all cases - - with the em- 

 bryonic course of development of the organ. 



In connection with what has been mentioned about BEIJERINCK'S 

 ideas on the formation of galls, and what we are going to observe 

 about his ideas on the development of adventitious buds, we wish to 

 emphasize the way in which BEIJERINCK'S ideas in this treatise al- 

 ready coincided with those of SACHS, who supposed that special 

 substances were required to produce special formations. With respect 

 to the formation of ascidia, due to the growing-together of two leaves, 

 or to deformation of a part of one leaf, BEIJERINCK observes, for 

 example : "It appears that one must suppose in all these cases that the 

 direct cause of the anomaly is due to a diminishing of the quantity of 

 the "stem-forming substance" in the vegetation point, which causes 

 at the same time a cessation of the normal relations between this 

 material and the "leaf-forming substance"; in the case of ascidia, 

 which are only appendices of leaves, it must be supposed that a change 

 in the relation between the quantities of the different substances out 

 of \vhich the various parts of the leaf develop acts in a similar way. 

 If the quantity of stem-forming substance is suddenly greatly decrea- 

 sed, then the leaf-forming substance will be present in such a quantity 

 that the whole region around the vegetation point will be occupied by 

 it, resulting in the development of an ascidium". 



To forestall the possible criticism that BEIJERINCK found satis- 

 faction in the formulation of hypotheses, we shall quote here his final 

 sentence: "It must be recognized that everything which is stated here 

 about formation of ascidia is of a hypothetical character, and does 

 little to satisfy the mind", of which the last phrase especially is 

 characteristic of a man who is content only when hypothesis is confir- 

 med by experiment. 



In the meantime BEIJERINCK'S studies on adventitious organs 

 continued unremittingly; the results were finally set down in an 

 extensive publication appearing as a treatise of the Royal Academy 

 of Sciences in Amsterdam in 1 886, under the title "Beobachtungen und 

 Betrachtungen tiber Wurzelknospen und Nebenwurzeln" 1 ). Many of 



!) Verhandelingen der Koninklijke Akademie van Wetenschappen Amsterdam 

 25, 1886 (Verzamelde Geschriften 2, 7121). 



