Dr. Allemao on the Origin of Vessels in Plants. 217 



condition of the branch. Applying this fact to the case of the liga- 

 ture, he thinks it evident that the cambium or elaborated sap, or 

 whatever may be the source of the tumour deposited between the 

 wood and the bark, must assuredly proceed from the leaves towards 

 the root, and meeting with this obstacle, becomes accumulated there ; 

 its tendency to organize itself not being distributed, a zone of adven- 

 titious or occasional vital centres soon appears in that point, whose 

 two forces are quickly manifested ; the ascending fibres continue to 

 extend themselves without impediment, while those which should 

 have descended, unable to overcome the impediment presented to 

 their further progress, continue to grow, twisting and interlacing 

 themselves, so as to form a tumour. 



Mr. Miers then refers to the differences which Dr. Allemao be* 

 lieves to exist between his theory of the evolution of each fibre in 

 opposite directions upwards and downwards, and that of Gaudichaud, 

 in respect to which he thinks there must be either a misprint or a 

 complete misapprehension of the views of Gaudichaud, who clearly 

 traces the source of each bud, not from the point of external growth 

 (as Dr. Allemao seems to infer), but from the seat of its origin 

 around the medullary sheath, at the noeud vital or point of de- 

 parture of each independent ascending and descending system of 

 vascular fibre. The origin of numerous distinct bud-formations 

 around the medullary sheath, and the extension of ascending spiral 

 vessels and of corresponding descending dotted vessels from each of 

 these separately, are maintained throughout by Gaudichaud in his 

 " Recherches Generales" as an essential part of his theory, and mi- 

 nutely demonstrated in his figures, both in monocotyledonous and 

 dicotyledonous plants. He even forcibly quotes the same circum- 

 stances of the intumescence of a stem produced by a ligature, and 

 the germination of an apparently budless stem, in support of his 

 views; between which and those of Dr. Allemao, Mr. Miers is con- 

 sequently unable to perceive any essential difference. 



Mr. Miers further quotes, from early works of Mirbel, the proof 

 that, as long ago as 1802 and 1809, he accurately depicted and de- 

 scribed the origin and formation of similar vessels in germinating 

 seeds of Nelumbo and of the Common Haricot ; and refers to plates by 

 him in the 5th and 13th volumes of the ' Annales du Museum,' 

 showing the ascending system of spiral vessels in the plumule and 

 cotyledons, and the descending system of dotted vessels in the 

 radicle. 



Dr. Allemao further states, that although the " bolbo radicular " is 

 always the chief growing point of the radicle, he observed, in Euphor- 

 hiacecB, four other cruciform branches, on the same horizontal plane, 

 proceeding from this radicle. The same fact was described more 

 than forty years ago by Auguste de St. Hilaire (Ann. du Mus. xix. 

 p. 467) in the germination of a Ranunculaceous plant {Ceratoce- 

 pJialus). In this, besides the main shoot, growing in the same way 

 as an ordinary exorhizal root, five other branching rootlets are 

 shown to be produced on one plane, from the collar of the young 

 root, which make their appearance through lacerations of the ex- 



Ann. ^Mag, N. Hist, Ser. 2. Vol xvi. 15 



