THE PALM-STEM. 39 



lying in front of this bundle of proper vessels in the 

 Monocotyledons, is not to be referred to the wood, but to 

 be considered as the liber of these plants. 



On the other hand must be mentioned, as distinctions 

 in these structures : 



1. That in the Dicotyledons, the formation of the vas- 

 cular bundle is not concluded with the development of 

 the Corona., as in the Monocotyledons. 



2. That in very few Dicotyledons is there a bundle of 

 proper vessels between the liber and wood. 



3. That in most Dicotyledons the liber-bundle is sepa- 

 rated from the wood-bundle by some layers of cells; that 

 it does not exhibit such different degrees of development 

 in different parts of the bundle ; and that it never attains 

 to such considerable firmness and size, as in many 

 Monocotyledons. 



It has already been observed that, besides the proper vessels, milk-vessels 

 are met with in many Monocotyledons ; the same occurs in many Dicotyle- 

 dons ; for instance, in the Umbelliferse, where milk-vessels lie among the 

 proper vessels in the wood-bundle, as well as in the pith and rind, while the 

 milk-vessels of the Dicotyledons, e. g. in Euphorbia, Asclepias, Morus, Acer, 

 Sambucus, &c., scarcely ever occur in the vascular bundles, but only in their 

 vicinity, in the bark and pith. (See Bernhardi, iiber Pflanzengefasse, p. 53 ; 

 Treviranus, Beitrage, p. 44; Moldenhawer, p. 126.) 



Comparison of the Palm-stem with the Stem of 

 Dicotyledons. 



So long as Desfontaines' theory, that the young vascu- 

 lar bundles of the Palm-stem originate in the centre, is 

 believed to be correct, no parallel can be drawn between 

 the stem of Palms and of Dicotyledons, for in such a con- 

 dition these stems would exhibit only distinctions, but no 

 resemblances. Since, however, the course of the vascular 

 bundle is quite different from what was formerly sup- 

 posed, and since its structure agrees perfectly with that 

 of the vascular bundle of the Dicotyledons, it appears to 



