In 1902 BEIJERINCK wrote a short communication for the first 

 number of the journal "Marcellia" '). For more than 20 years the 

 Kollari-gall had intrigued him. He had stated in 1882, as has been 

 told above, that the inhabitant of Cynips Kollari, reproducing par- 

 thenogenetically, would produce new Kollari-galls onQ.pedunculata, 

 but afterwards he began to doubt his own observations. He repeated 

 the experiments from which he had drawn his conclusions, but the 

 expected results did not emerge. His experience with the Calicis-gall 

 led him, after many unavailing experiments, to isolate a few speci- 

 mens of Cynips Kollari ]ust out oi the chrysalis, together with a branch 

 of Q. cerris. Within one hour oviposition on the buds was observed: 

 "Alles war einfach und klar; die lange gesuchte Losung des Ratsels 

 war gefunden". Out of the infected buds of Q. cerris there developed 

 small groups of the Circulans-galls inhabited by Andricus circulans 

 which galls BEIJERINCK described in 1896. In this case too, therefore, 

 simultaneous existence of heterogenesis and heteroecism is highly 

 probable. One link in the proof is missing here however: BEIJE- 

 RINCK did not succeed in making the females of A. circulans lay eggs 

 in the buds of Quercus pedunculata. BEIJERINCK presumed that these 

 powerful insects have the custom to fly about for a long time before 

 copulating. He has not been able to observe the act of copulation. If 

 the presumption is correct, it would explain why the occurence of the 

 Kollari-gall is not bound up with the immediate presence of Q. cerris, 

 as appeared to be the case for the formation of the "Knopper-gall". 



The last word on this problem has certainly not yet been said. 



BEIJERINCK incidentally touched upon the subject of gall forma- 

 tion once more later on, but these later remarks attracted little at- 

 tention, partly because they appeared in a treatise in which one would 

 not expect to find such a discussion. The passage referred to is of such 

 importance for an appreciation of the development of BEIJERINCK'S 

 views that it merits an unabridged reprint. It is found in a treatise 

 published in 1917 entitled "The Enzyme Theory of Heredity" 2 ), and 

 reads as follows : 



"Long ago already I came to the conviction that the ontogenetic 

 evolution of the higher plants and animals can be best explained by 

 admitting that it is caused by a series of enzymes, for the greater part 

 endo-enzymes, which, becoming active in a fixed succession, determi- 

 ne the morphological and physiological properties gradually manifest 

 in the development. These enzymes in the formation of plant-galls are 

 likewise concerned, and in a study on the galls of the saw-fly Nematus 

 capreae on the leaves of Salix amygdalina, I gave them the name of 

 "growth enzymes". It is still my opinion that this view is in the main 



') Ueber die sexuelle Generation von Cynips Kollari, Marcellia, Padova 1, 13-20, 

 1902 (Verzamelde Geschriften 4, 133-138). 



2 ) Proceedings of the Section of Sciences, Kon. Akademie v. Wetenschappen Am- 

 sterdam 19, 1275-1289, 1917 (Verzamelde Geschriften 5, 248-258). 



