402 H. von Mohl on the Cambium-layer 



energy of the cambium is lost before it arrives at a condition to 

 form the wood-cylinder. In my ' Anatomy of Palms/ I took 

 these outer vascular bundles of Dracaena for the lower ends of 

 the bundles belonging to the leaves above, and Unger* was led 

 by his investigations to agree with this ; but I now think that 

 Karsten was right in stating this view to be erroneous. The 

 comparison made by Karsten (p. 103) between these outer bun- 

 dles and the annual rings of the Dicotyledons is less admissible, 

 since the latter, especially in our native trees, owe their origin 

 chiefly to the further development of the cambium situated upon 

 the individual primary vascular bundles between the wood and 

 the liber, and therefore are of essentially different derivation 

 from the outer vascular bundles of the Dracaena. More satis- 

 factory would be the comparison of these vascular bundles with 

 those layers of wood which, in many Dicotyledons with widely 

 diffused bundles, as in the Balsamineae, are developed from that 

 part of the cambium-layer which lies between the primary vas- 

 cular bundles ; and still more apt is the comparison with those 

 external woody bundles of the Nyctaginese, Chenopodese, &c, 

 sometimes arranged in concentric circles, and sometimes con- 

 founded into more or less irregularly arranged masses, which 

 Unger has so beautifully investigated, and which, in like man- 

 ner, have no relations with the leaves. Doubtless many analo- 

 gies might be made out between the organization of the stem of 

 the Dracaenae and that of the stems of many tropical climbers ; 

 but as I have no opportunity myself of following out the deve- 

 lopment of the latter forms, I shall not enter upon this point. 

 The outer bundles of the Dracaena contain no vessels, their ele- 

 mentary organs corresponding rather with those of which the 

 liber-bundles of the Monocotyledons are composed. Hence it 

 may appear doubtful whether they are comparable at all with 

 the vascular bundles ; but this objection appears of small weight 

 when we bear in mind that the same anatomical characters are 

 frequently found in the lower portions of all the vascular bundles 

 of Monocotyledonous plants. In fact, this circumstance was 

 one of the reasons for my regarding these bundles as the inferior 

 prolongations of those bundles passing out into the leaves higher 

 up in the stem. 



Schacht attempted to extend the theory of the cambium -ring 

 and its development into wood by setting up a series of special 

 laws (while he coincided in general with Karsten's views), in 

 obedience to which the development of the different portions of 

 the stem should take place. Whether his attempt was a for- 

 tunate one, will appear from the sequel. 



One of the most general of these laws (' Pflanzenzelle/ p. 255) 

 * Bau u. Wachsthum d. Dikot. Stammes, p. 37. 



