54 



by submerging the part of the plant with the ovnlating insect in ether, 

 resulting in the immediate death of the insect before withdrawing its 

 ovipositor. By dissecting the plant-organ carefully, the method of 

 ovipositiori could be determined exactly. Of these observations 

 drawings were made which, especially, are greatly to be admired. 



BEIJERINCK even succeeded in dissecting an oak bud on which a 

 specimen of Biorrhiza apt-era was in the act of oviposition, and in 

 observing, by means of a magnifying glass, the discharge of an egg 

 from the ovipositor. In this way he was able to explain completely the 

 remarkable manner in which the egg passes through the narrow chan- 

 nel of the ovipositor. 



From BEIJERINCK'S observations still one other point was of 

 especial interest, namely, that the eggs of some gall-wasps are deposi- 

 ted within the plant tissue by means of the ovipositor, but that they 

 are deposited by other gall-wasps on the surface of the undamaged 

 epidermis of the plant organ. The latter happens for instance with the 

 egg which the Folii-wasp, emerging from our common oakleaf-gall, 

 deposits in a small dormant bud at the base of the trunk of the tree. 

 The wasp bores with its short ovipositor through a great number of 

 bud scales, but deposits the egg on the top of the growing point, to 

 which the egg is fastened with a small quantity of mucous secretion. 



BEIJERINCK concluded from his observations that the abnormal 

 cell-growth which causes the Cynipidae-galls was due neither to an 

 injury, nor to a poison brought into the wound or into the epidermis 

 by the oviposition. The changes of the normal tissue after this opinion 

 start as a result of the "Larvenentwicklung". BEIJERINCK supposed, 

 however, that the stimulation can sometimes become noticeable 

 while the larva is still in the egg. In the first stage of development of 

 the gall no mechanical damage of the tissue by the larva should occur. 

 If the ovum was deposited on the surface of a tissue it should become 

 enclosed by "Umwallung" as a result of the cell division in the neigh- 

 bouring tissue. 



Later on it appeared that BEIJERINCK'S notions on these points 

 needed alteration. Presumably, the injury plays a greater role than 

 BEIJERINCK supposed, and it is now agreed that the larva produces a 

 larval cavity by sinking into the tissue lying beneath it, which is 

 killed by its secretions, this means that the "Umwallung" is apparent 

 only. This was proved in 1911 by WEIDEL i) for the gall of Neuro- 

 terus numismalis , and in 1914 by MAGNUS 2 ) for other Cynipidae-gaH.s. 



This need of alteration, however, refers only to a part of the devel- 

 opment, and later investigators unanimously praise the exact manner 

 in which BEIJERINCK has described the later stages of growth of Cy- 



!) F. WEIDEL, Beitrage zur Entwicklungsgeschichte und vergleichenden Anatomie 

 der Cynipidengallen der Eiche, Flora 102, 279-334, 1911. 



2 ) W. MAGNUS, Die Entstehung der Pflanzengallen verursacht durch Hymenopteren, 

 Jena 1914. 



