of the Stem of the Phanerogamia. 395 



at an end at that part of the stem where the lower end of the 

 bundle lies, but increases more and more upwards ; whence, in 

 examining full-grown stems, the lower end of the individual 

 vascular bundles are found at the outward boundary of the me- 

 dullary parenchyma, and mostly covered only by a couple of 

 layers of cells which belong to the latter tissue, while the upper 

 part of the bundle, which at its origin is only separated from 

 the centre of the stem by a small and no longer multiplying 

 number of cells, and is subsequently covered on its outer side 

 by thick layers of cells, is found deeply seated in the stem. 

 The uppermost extremity, lastly, which already in the bud is 

 connected with a leaf, in the further development of the bud 

 must follow the leaf in proportion as this is pushed outwards 

 from the centre towards the cylindrical periphery of the stem, and, 

 in the same proportion as the cellular tissue is multiplied at the 

 circumference of the stem, undergo an intercalary growth between 

 the centre of the stem and the base of the leaf, and assume a 

 more or less horizontal course from within outward. Since the 

 same process is repeated in the cambium-cone pushed further 

 out towards the periphery, the younger bundles, which originate 

 in the expanded cambium-mantle, must run separate from the 

 older, and further out in the stem. If, as is often the case in 

 the Palms, both earlier- and later-formed bundles enter the same 

 leaf, the place of the curvature into the leaf of the younger 

 bundles will be found not so deeply seated in the full-grown 

 stem as that of the older, because, at the time of their first 

 development, the base of the leaf and the cambium-cone were 

 already further removed from the centre of the stem, by the 

 production of medullary cells, than at the formation of the older 

 vascular bundles running into the same leaf. This condition 

 was first made out and rightly explained by Meneghini. 



Schleiden was well acquainted with this diverse mode of deve- 

 lopment of the Monocotyledonous and Dicotyledonous bundles ; 

 unfortunately, he adopted the notion that this was altogether 

 independent of the circumstance whether the plant belonged to 

 the Monocotyledons or Dicotyledons, but stood in connexion 

 with the circumstance whether the internodes of a stem were 

 elongated lengthwise into a cylinder, or remained abbreviated. 

 In consequence of this, he fell from one error into another. 



The mode of development of a cylindrical stem mentioned by 

 him under b, in which the development progresses from below 

 upwards in horizontal disks, whereby the vascular bundles ac- 

 quire a straight direction and a position parallel with the axis, 

 does not exist at all. Every stem, be its form what it may, ter- 

 minates above in a punctum vegetationis, in which its leaves are 

 formed, and towards which its youngest vascular bundles con- 



