38 THE PALM-STEM. 



vessels, after the woody mass has increased in size by 

 further growth, that the wood-cells begin to arrange 

 themselves in regular rows. In front of the wood lies 

 a large bundle of proper vessels, which may be readily 

 distinguished from the parenchyma by their thin walls, 

 and the absence of chlorophyll-granules. This vascular 

 bundle is distinguished from that of the Monocotyledons, 

 by the fact that the liber does not stand in immediate 

 connexion with the vascular bundles ; but the liber- 

 bundles grow together in waving lines, and are separated 

 from the proper vessels by several layers of cells. We 

 find the same structure in the vascular bundle of Meni- 

 spermum canadense. 



Comparing the vascular bundle of the Monocotyledons 

 with that of the Dicotyledonous trees, we meet with a 

 great resemblance, the posterior portions of the wood 

 having the cells thin-walled, and placed in no regular 

 order. The smallest vessels lie farthest back, and are 

 spiral ; nearer to the front lie larger scalariform ducts, 

 and to these follow the large porous vessels. We do not 

 come to the firmer portion of the wood until we arrive 

 at the front of these, this wood being composed of thick- 

 walled cells lying in regular rows, and of porous vessels. 



From these facts it is most clear : 



1. That the vascular bundle of the Monocotyledons 

 exhibits the same composition, as that of the Dicotyledons 

 possesses in 'its earliest condition. 



2. That the part of the vascular bundle of the Palms, 

 which I, in spite of its having no ligneous solidity, have 

 denominated the wood, corresponds most closely with the 

 innermost part of the ligneous body of the Dicotyledons, 

 to which Hill applied the name of the Corona. 



3. That in many Dicotyledons, also, a bundle of proper 

 vessels lies between the liber and wood; besides the 

 plants named, this may be found in Spiraa Ulmaria, 

 Aruncus, Fumaria ojficinalis, Echinops, and Mimosa 

 pudica. 



4. That the portion composed of prosenchymatous cells, 



