58 



This treatise of 1 896 is worth studying not only on account of the 

 important findings which are discussed, but even more so because 

 here BEIJERINCK'S general considerations on gall formations reached a 

 culmination. Herein, for instance, full stress is laid on the remarkable 

 fact that the galls show a complete series of "adaptations" which 

 are of use to the insect enclosed (NEGER ') spoke of "altruistic adap- 

 tations" in similar cases later on), and which adaptations are in- 

 dispensable since the insect is exposed to attacks from an army of 

 enemies. BEIJERINCK again raises the question as to what mechanism 

 induces the plant-host to make these formations. He once more 

 concluded that there must be some matter which can move freely 

 from one cell to another, and which determines the formation of the 

 developing gall. Since he imagined that the protoplasm does not leave 

 the cell, he supposed that this matter is produced by the larva or is 

 brought along as a poison with the egg by the mother insect. Thus 

 BEIJERINCK comes again to the conception of the co-operation of a 

 growth-enzyme . 



BEIJERINCK in this publication draws a further conclusion. He 

 considers it as very probable that there exists no essential difference 

 between the development of meristematic tissues into the full-grown 

 organs of restricted growth and the development of a tissue by cell- 

 division into a gall. When this is right, then with normal ontogenesis 

 too there must be acting a circulating or diffusing substance which 

 determines the form and the physiological function of the developing 

 tissues. The morphological changes caused by this substance which 

 determine the restricted development of the organs should, to a cer- 

 tain extent, act in opposition to the tendency possessed by the cells 

 to transmit their properties unchanged to the daughter cells. 



The point of view indicated here is considered of paramount 

 importance by BEIJERINCK not only for the ontogenesis but for phy- 

 logenetic development also. The occurrence of mono-cellular variabili- 

 ty in this development he believes to be the rule (nowadays this 

 would be called mono-cellular mutation), but he takes the gall 

 formation as proof that multi-cellular variability can also be active. 



It is typical of BEIJERINCK that somewhere in the middle of this 

 treatise he deplores the unenthusiastic reception which he feared these 

 novel ideas were to meet. The convincing power - - says BEIJERINCK 



- of the exposition of a law of nature is less determined by the cor- 

 rectness of the law than by the way it harmonizes with current 

 opinions. However, the end of this treatise, which BEIJERINCK, when 

 he wrote it, probably believed to be his last publication on galls, is 

 very cheerful as to the wide prospects which the study of galls opens 

 up. He calls them "formations which cast a new light on the laws of 

 organo-genetics and of variability". 



!) FR. W. NEGER, Biologie der Pflanzen auf expL-rimenteller Grundlage, Stuttgart 

 1913, p. 533. 



