Dr. Wiltshire's Contributions to Structural Botany. 85 



maintained that the vascular or woody portions of the inter- 

 nodial spaces were continuous, and the state of articulation 

 was solely dependent upon the non-continuity of the vessels 

 of the bark. Dutrochet again averred before the French 

 Academy that his views were right. Here I believe the 

 matter has rested. I have taken some pains to satisfy my- 

 self which of these theories is correct. I have examined por- 

 tions of the plant both young and old, and at all portions of 

 the nodal places, and I fully concur with Decaisne in stating 

 that the true woody and vascular structure of Viscum is per- 

 fectly continuous through the nodi ; that there is no trans- 

 verse and separating layer of cellular tissue or pith in this 

 portion of the plant, but that the connexion of the inner 

 layers of the bark is broken up at the nodi. Viscum album 

 has not an articulated stem, in the proper sense of the word 

 then. The vascular structure of Viscum album is by no 

 means so entirely composed of those peculiarly marked and 

 rather elongated cells as is generally drawn and stated. Kie- 

 ser's representations are often copied, but they only repre- 

 sent a part of the vascular apparatus ; no doubt a great por- 

 tion of the woody matter is composed of cells quite different 

 from those met with in the wood of Exogens ; but if the 

 young wood or first-formed bundles be examined, plenty of 

 very long annular ducts — and (to me) spiral ducts, with the 

 fibre unrollable, however, as far as I have been able to de- 

 tect — will be found. I may also remark, that the long pa- 

 renchymatous cells surrounding the first-formed vascular 

 bundles are carried along with the latter to the centre of the 

 plant, around the pith of which they may be found, — a circum- 

 stance somewhat analogous to that stated by Decaisne to 

 take place in Menispermacece. 



3. — There are very few plants, in the anatomy of whose 

 pleurenchymatous and vascular structure a stronger sup- 

 port for some of the views of Schleiden on the origin of spi- 

 ral structure, Sec. can, I think, be seen, than in Tilia eu- 

 ropcea. The anatomy of the tissues of this plant appears to 

 me to prove that primary membrane is homogeneous and 

 structureless, but that the secondary formations of tissue 

 ensuing within cells composed of such primary membrane 

 are in their form and nature fibrous, and in their direction 

 spiral. Out of such secondary structure the origin of all 

 tissue presenting a fibrous appearance, and the least tendency 

 to a spiral direction in any period of its growth or develop- 

 ment, is to be looked for. In this plant, as also in many 

 others of the families Asclepiadacea and Apocynece, it ap- 

 pears evident, that in the development of the primary fibrous 

 layers, two fibres having opposite directions are formed ; but 



