55 



nipidae-galls. Magnus, the investigator who after Beijerinck 

 studied the origin of Cynipidae-gaïls most fully, refers in his pubHca- 

 tion, in which he disagrees on several other points with Beijerinck's 

 opinions, to the "klassischen Arbeiten Beijerinck's". He also gives 

 further evidence of his highest appreciation by beginning the de- 

 scription of his own observations on the TerminaUs-gall with the 

 words: "Die Biologie dieser Galle hat durch die bewundernswerten 

 Beobachtungen Beijerincks ihre volle Aufklarung gefunden". 



The admiration which even now every expert feels on reading 

 Beijerinck's treatise, is due in the first place to the fact that a man 

 was writing who possessed an unusually extensive knowledge of all 

 the subdivisions of the wide field covered by cecidology, viz., ecology, 

 systematics, morphology, teratology, genetics, anatomy, and animal 

 and plant physiology. 



Beijerinck's next treatise on galls, dating from 1885, dealing 

 with the gall caused by Cecidomyia Poae on Poa nemoralis i), may 

 be considered as a continuation of his great work on galls, and is 

 inspired by the same spirit. This study derives a special importance 

 from the proof that the remarkable appendages developed at the 

 stem of Poa nemoralis under the influence of the larva, are real 

 adventitious roots. It is true that they develop at very unusual 

 places on the stem, but they have the structure common to all such 

 roots, and they can develop into normal roots with lateral roots 

 if the gall-bearing part of the stem is planted as a slip. Beijerinck 

 attached hereto the far-reaching conclusion : "dass pflanzliche Gewe- 

 be, welche die Fahigkeit zur Bildung normaler Organe nicht besitzen, 

 diese Fahigkeit durch die Aufnahme von aussen kommender Stof f e 

 erlangen können". 



We mention further a lecture 2) held by Beijerinck in the same 

 year on the subject of galls on Cruciferae, in which he gave a survey 

 of these galls only, without going into further detail. 



Of much greater importance is Beijerinck's treatise of 1888 

 "Ueber das Cecidium von Nematus Capreae auf Salix amygdalina" 3). 

 The importance of this publication is less due to the very careful 

 description of the gall-insect (this time of the f amily Tenthredinidae) , 

 of the manner in which the leaf is injured by the insect, and of the 

 structure of the gall, than to the importance of the considerations on 

 the nature of the gall formation. 



In this treatise Beijerinck dealt with the question as to whether 

 the substance which causes the formation of the gall produces a 

 permanent change in the protoplasm,. or whether the change is only 



1) Die Galle von Cecidomyia Poae an Poa nemoralis. Entstehung normaler Wurzeln 

 in Folge der Wirkung eines Gallenthieres, Bot. Zeitung 43, 306-315 and 320-331, 1885 

 {Verzamelde Geschriften 1, 386-400). 



2) Over gallen aan Cruciferen, Ie Bijlage tot de 30e Jaarvergadermg der Nederl. 

 Bot. Vereeniging 1885 (Verzamelde Geschriften 2, 1-6). 



3) Bot. Zeitung 46, 1-11 and 17-27, 1888 (Verzamelde Geschriften 2, 123-137). 



