418 CONSERVATIVE ORGANS. [_LECT. VIII. 



consideration only, I should have adopted his 

 opinion, as it is the innermost and apparently 

 the least perfect of the series in each fasciculus: 

 but having seen it, in a more perfect form, in 

 the Tradescantia ; and not being able to con- 

 ceive why those distinct rings should exist only 

 to be transmuted into punctuated spirals, I am 

 inclined to consider it a distinct vessel. It is 

 true, as Kieser has observed, that the mem- 

 branous vessel, or intervening membrane as he 

 terms it, is punctuated ; but he appears to have 

 overlooked the fact, that the rings are retained 

 in their places by minute acicular bodies, which 

 I have separated from the vessels in Tradescan- 

 tia, although I have not succeeded in doing so 

 from those in the Bryony. No such bodies are 

 seen attached to the real annular vessel ; and in 

 the spiral vessel (Plate 8, fig. 5, #.), which is the 

 intermediate of the large annular vessel and the 

 ringed membranous vessel in the Bryony, the 

 * flattened fibre or fillet forming the spirals is 

 itself punctuated. Notwithstanding, therefore, 

 the apparent probability and simplicity of Kieser's 

 theory of the transformation of the ringed mem- 

 branous vessel into the punctuated spiral ; and 

 this into the annular, in the description of stem 

 now under consideration ; I am still of opinion 

 that the central vessels, in the vascular fasciculi in 

 the stem of Bryony and of similar plants, are of 



