Vegetable Physiology for the Year 1836. 67 



of the branches. These several kinds of ramification also 

 contribute in various ways to the enlargement of the stem. It 

 must be entirely ascribed to this, if they follow the already 

 completed vegetation of the main axis; they only take a small 

 part in it, when they rise from the inflorescence to the angle 

 of the leaves then present. 



We must establish similar distinctions with regard to the 

 roots ; for when they hang down from the basis of the stem, 

 their vascular bundles are continued ; when, on the other 

 hand, they break out from the lateral parts, they send forth 

 their formations of vascular bundles between the ligneous body 

 and the exterior layer of cortex. 



5. What new distinctive characters are established by 

 means of these organic properties between the stems 

 of the two great classes of phanerogamic vascular 

 plants ? 

 A parenchymatous cellular tissue, through which vascular 

 bundles run longitudinally, forms the organization of the stem 

 of a dicotyledonous, as well as of a monocotyledonous plant 

 in the first periods of life. The internal structure and the 

 relative arrangement of these fibres must remain subjects of 

 comparison. As to the structure, Mohl proved that it is the 

 same in both classes. We find in the monocotyledons as in 

 the dicotyledons, on the inner side of the vascular bundle, 

 which is directed towards the axis of the stem, a chain of 

 vessels, which form a part of what is called by Hull corona ; 

 by botanists of the present day medullary sheath in the 

 wood of dicotyledons. The exterior side of the bundle is on 

 the other hand occupied by prosenchymatous cells, and these 

 are those which in dicotyledons form the liber. Lastly, be- 

 tween the inner ligneous layers and the exterior bundles of 

 liber is another bundle of distinct vessels, which in its pro- 

 portion is variable, and at times is even wanting in dicotyle- 

 dons. In this the indicated structure is still the same in the 

 whole course of the single ligneous bundles; different, how- 

 ever, in the various progressions of its course in the stems of 

 monocotyledons. 



The direction also of the ligneous bundles in these plants 

 is different at different points of the stem, while in the dicoty- 

 ledons they descend perpendicularly, and always parallel with 

 one another. Great diversity may however be remarked 

 during the progress of vegetation. In the monocotyledons the 

 constant isolation of the fibres allows of every one of them re- 

 peating, with each fibre, in their two courses, the same pecu- 

 liarity reversed ; the more recent the upper course, the nearer 



K2 



