252 Meyen's Report for 1839 on Physiological Botany. 



tain that spiral vessels are indifferently wound either right or 

 left. He finds left-wound vessels so extremely rare, that they 

 may rather be regarded as exceptions to the rule. In a vas- 

 cular tube in a gourd, M. Mohl saw that the different divi- 

 sions of the spiral fibre which are separated from each other 

 by rings were wound in opposite directions. 



M. Schleiden demonstrated his new view of the formation 

 of the annular ducts principally by means of the young shoots 

 of Camjjelia ; M. Mohl found, however, the roots of Commelina 

 tuberosa much better, and gives excellent figures on the sub- 

 ject. All the modifications which have been observed under 

 M"hich the rings appear in the vascular tubes of this plant are 

 fully described, and their connexion with the spiral fibre ex- 

 plained. According to my idea, M. Schleiden had quite cor- 

 rectly stated that the line of division in the broad spiral fibres 

 of the Commelinece is caused by two whorls of the fibre grow- 

 ing together, or in other words, that those spiral fibres con- 

 sist of two fibres which lie close and parallel to each other ; 

 however M. Mohl makes objections to this, but which I can- 

 not quite clearly understand. 



M. Mohl found, as others have done, that the rings in the 

 annular tubes are generally quite unconnected with each other, 

 but that the connecting fibres of the rings (when such exist) 

 do not stand in any determinate relation to the breadth 

 of the annular fibres. [This is however in general the case 

 only in the broad and compound spiral fibres of the Comme- 

 linecE. — Mey-I During the formation of the annular tubes in 

 the stem of CommeJina tuberosa, M. ]Mohl thinks that he ob- 

 served distinctly that these tubes at their first appearance 

 were not spirally wound, but that the fibres formed, as in the 

 perfect vessels, isolated rings of different breadths, or else rays 

 between which were seen some spiral fibres, so that, with ex- 

 ception of the small thickness and the short distance between 

 the rings, there was no difference between these young ves- 

 sels and the fully developed ones. This formation could be 

 still better followed, step for step, in the roots of the Comme- 

 lina ; and from these observations M. Mohl draws the conclu- 

 sion, that annular ducts, spiral vessels, and reticular vessels 

 are three very nearly related forms which pass into each other, 

 but that they cannot be regarded as temporary grades in the 

 metamoi'phosis of the same vascular tube. 



Much has been said in the former reports concerning this 

 metamorphosis of the spiral into annular fibres, and it is to be 

 hoped that the discussion will soon be ended ; all that M. Mohl 

 has brought for\Aard against the new theory of Schleiden I 

 myself can fully confirm, if that were necessary, both by former 



