84 DUCTS MOH1/S VIEWS. [BOOKI. 



with the results of an examination of the developed organ. 

 Now, in the present case this contradiction assuredly exists 

 between the structure of the developed annular vessels and 

 the theory of Schleiden. 



" Let us now see what information the examination of the 

 young vessels gives us of the mode of their development. 

 At first I selected the stems of different plants, especially 

 of Tradescantia tuberosa, because Schleiden announced 

 that he had remarked the metamorphosis of spiral vessels 

 into annular vessels in the youngest internodes of subter- 

 ranean and ascending stems. The results have not been 

 favourable to the theory of Schleiden. For this examination 

 it is not proper to select vessels placed at the interior angle 

 of the vascular bundles, because these pass too rapidly through 

 the phases of their development, and their diameter is also 

 too small ; the coils of their fibres being, moreover, at first 

 too close together to allow any observations made upon them 

 to be considered as conclusive. The larger vessels, placed 

 more towards the exterior, present less difficulties in these 

 respects, though here also an unfavourable circumstance 

 occurs, viz., that the rings in the course of their development, 

 in consequence of the feeble longitudinal growth of the vas- 

 cular utricles, remain very close together, which may, in 

 some cases, render the distinction of the annular and spiral 

 formations in the fibres difficult, and which, in all cases, 

 makes it rather hard to decide whether there does or does 

 not exist between each pair of rings a slender spiral fibre, 

 which is subsequently absorbed. However, I think I have 

 observed with certainty, that from the beginning, and so soon 

 as I could distinguish the fibres on the interior surface of the 

 vascular utricle, under the form of thin, more or less narrow, 

 diaphanous edges, they were not absolutely spiral ; but that, 

 as in the developed vessels, they formed either complete 

 isolated rings, or rings intermixed with spiral fibres ; so that, 

 with the exception of the thinness of the fibres, and of the 

 small distance of the rings from each other, there is no 

 essential difference observable between them and the per- 

 fectly developed vessels. 



" The examination of the vessels of the stem not having, 



