356 NATURAL SCIENCE. Nov.. 



stem and leaves and blossoms, as otherwise they would do, to group 

 themselves about this foreign organism, in radial and concentric 

 layers, each endowed with new and peculiar properties, each destined 

 to perform a new and special office ? 



Attempts have, of course, been made to answer these and 

 cognate questions ; but the explanations have, in great part, been 

 little more than crude conjectures ; and in no case, so far as I know, 

 have they been of a character to meet, in any complete degree, the 

 scientific requirements of the problem. 



Redi 5 — who, like Von Helmont and the other vitalists, explained 

 all organic phenomena by reference to the guidance of a distinct 

 spiritual entity or Archaeus — believed in a vegetative soul in each 

 plant. This soul he considered presided at the formation of the egg, 

 the insect, and the gall ; and so determined their specific characters 

 and their several relationships. Such views, at this day, we shall 

 find it difficult to appreciate. They are, as Lucaze Duthiers has said, 

 but the dreams " de I'esprit philosophique d'un autre temps." ^ 



Reanmur, whose " Memoirs pour servir a I'histoire des Insects," 

 (published A.D. 1738) contain so many curious and interesting 

 details, was early led to refer the growth of galls to the suction of 

 insects, having been himself much impressed by those produced by 

 Aphides on the leaves of elms and limes. This suction, he believed, 

 determined an increased flow of sap to the part affected, and, as a 

 consequence, excess of vegetation and the production of the gall. 

 As, however, both original puncture and subsequent suction not 

 unfrequently take place in plants without any gall resulting, or 

 without, in fact, any hypertrophy whatever, this can scarcely be 

 regarded as the true explanation. 



Neither, as Reaumur also supposed, 7 can the increased heat 

 evolved by the developing egg be looked upon as a sufficient cause of 

 the growth of the gall, inasmuch as no development, in the sense in 

 which he used that term, takes place in the embedded ovum. 



Malpighi,^ who gave some considerable study to this subject, 

 assumed a fermentation to be excited in the acid of the oak by the 

 poison of the Cynips, and in this way sought to account for the 

 production of the gall. He, however, like Redi and other of his 

 contemporaries, was largely influenced by the prevalent spirit of the 

 times, which saw, or thought it saw, fermentations in all things. 



Lacazc Dnthicrs, whose " Researches on Galls," published in the 

 Annates des Sciences Naturelles for 1853, give evidence of much pains- 

 taking study of this subject, adopts the hypothesis of a specific 

 poison, a special lignis virus, as the main cause of the gall. It is, he 

 says, a fact that all Hymenoptera have a poison gland connected 



''Redi, born A.D. 1626. 



" " Recherches pour servir a I'histoire de gallas," par M. Lacaze Duthiers. 

 Ann. des Sci. Nat., 3rd series, Botanique, vol. xix., pp. 284, published 1853. 

 7 See " Memoirs," vol. iii., p. 478. ^ A.D. 1628-94. 



