250 Meyen's Report for 1839 on Physiological Botany. 



2. A circumstance which need only be cursorily mentioned 

 here is the form of the cells in the different intervening steps 

 in combination with the actual perforation of the primary 

 membranes by resorption. 



3. Another circumstance is more important. Generally 

 several spiral deposits appear, and the rule is here that the 

 succeeding deposits are arranged conformably with the pre- 

 ceding ones ; however some exceptions are known, as for in- 

 stance, after the first spiral deposit has become changed by 

 the extension of the cell, a new layer is deposited over the 

 •whole inner surface and assumes the porous form. The dif- 

 ferent metamorphoses which are exhibited in such a striking 

 manner by the spiral tubes in the fibro-vascular bundles of 

 Monocotyledons, are explained by the author as resulting from 

 a different extension of the several single elementary organs 

 of these bundles. The distant banded annular vessels are said 

 to be formed first, and in the form of spiral vessels ; by the 

 extension of the internodium the development is said to ex- 

 tend towards the exterior, and therefore the outer spiral tubes 

 are wound so closely because the extension of the cells longi- 

 tudinally is already nearly completed when the spiral depo- 

 sits take place. 



M. Schleiden comes next to the explanation of the produc- 

 tion of the annular ducts, concerning which there has been so 

 much written and disputed : he thinks that he has observed 

 that the annular vessels are the cells in which the spiral de- 

 posits are earliest formed. 



By drawings from the bud of Campelia Zannonia, Rich., M. 

 Schleiden endeavours to explain the production of the annu- 

 lar ducts ; they are formed out of spiral vessels : two whole 

 whorls of the spiral fibre grow together and form a per- 

 fect ring, while the connecting ends of the fibre are corroded 

 and at length completely absorbed by the cell ; all the stages 

 of transition are often visible in one and the same vessel, but 

 in more advanced vessels the connecting volution is wholly dis- 

 solved. This is M. Schleiden* s new hypothesis ; I have read 

 it through several times, but am not able to form an idea 

 how rings can be produced from spiral volutions, if the free 

 (eroded, or torn off, or absorbed) ends of the single whorls of 

 the late spiral fibre do not join together. In the porous cells 

 of the Coniferce M. Schleiden thinks he has seen, in Pinus syl- 

 vestris, even in the latest zones, the cambium-cells before the 

 formation of pores divided by fine black lines into narrow spi- 

 ral bands, and these vanish when the pores are formed ; of 

 course, adds M. Schleiden, the primary wall of the cell being 

 perfectly homogeneous. [I may be allowed to ask here, how 



