70 Prof. Meyen's Report of the Progress of 



number in the intermediate parts, as was also observed by 

 Meyer. This is most easy to examine in those species of 

 Piper where the stem is herbaceous and fibrous, &c. 



From a combined consideration of these observations we 

 obtain the following positions: — 



The bipartition of the vascular bundles by means of the 

 intermediate formation of new fibrous vascular bundles, and 

 the subsequent increase of the stem in breadth, belongs solely 

 to the dicotyledons. On the other hand, the increase in thick- 

 ness which is formed by the superposition exteriorly of new 

 fibrous layers on those already present, is quite independent 

 of the medullary rays, and belongs in common to the mono- 

 cotyledons. In the dicotyledons the fibres immediately cease 

 to stand in relation to the leaves to which they belong, and 

 never remain connected by their rudiments. Each fibre loses 

 very soon its own individuality, as it divides itself into its ele- 

 ments, which then form a part of the two systems, &c. But 

 in the monocotyledons each fibre retains permanently and in- 

 variably its individuality. It remains independent of the leaf, 

 and follows all its movements as long as it has life. When 

 that is destroyed, it remains dependent on the cicatrix which 

 has been left on the exterior surface, and continues perma- 

 nently in connexion with it, as it extends itself gradually quite 

 through the new productions, which are constantly augment- 

 ing the thickness of the stem. 



6. What is to be added to the discoveries of Mohl with 

 respect to vegetable anatomy ? 



Mohl observed the course of the ligneous bundles in the 

 various stems of palms, by determining their deviations in the 

 vertical direction. He showed that all vascular bundles which 

 belong to SifiabeLlum (?) ( JVedel), while it occupies the outer end, 

 forms an elongated cone on the outer surface of the stem, the 

 apex of which opens at the development of the new leaf, as the 

 vascular bundles now diverge from one another to the peri- 

 phery, from whence they intersect with the latest formed ones, 

 &c. In order to inquire into the cause of this circumstance, we 

 must follow the leaves in their successive changes ofplace,apply 

 it to the changes of place which are imparted to the fibres, and 

 we must recognise the constant relation of the division of the 

 external organs to those of the inner vascular bundles. We 

 must, above all, distinguish the cases, in which the partition 

 of the leaf-stalk retains its original relations to the periphery; 

 of the stem, from those of an uncommon swelling of the latter, 

 by which the basis of the leaf-stalk is reduced to one, more or 

 less restricted, arc. Causes of this modification, if we take it 

 well into consideration, explain all differences which we may 



