210 EXTRACTS AND ABSTRACTS FROM FOREIGN JOURNALS. 



prismatic, and which, by their junction, form a continued whole ; and 

 in a morphological point of view, they are distinguished by this alone, 

 perhaps, from the analogous spiral cells. 



Two propositions, then, may be stated : 



1 . That the wall of the vessels is like that of cells originally, homo- 

 geneous. 



2. That the organization of the vessels, at their first origin, consists 

 in cells arranged in a linear series. 



M. Unger's conclusions are founded, principally, on observations upon 

 the organization of the radical extremity, and especially of that of the 

 fibrous roots of monocotyledonous plants. 



He preferred for this purpose the sugar-cane. 



Every fully-developed root presents in its interior a medullary part, 

 surrounded by a vascular, or ligneous one, and externally a cortical. 

 All these parts from the summit to the base preserve the same re- 

 lative position with respect to each other. During the growth of the 

 root, the medulla undergoes the least change ; the bark rather more, and 

 the vascular part by far the greatest ; and it is to the changes in this 

 part that the paper more particularly refers. 



The ligneous substance of the root, like that of the trunk, is formed 

 of vessels and of elongated cells, with walls of greater or less thickness. 

 In the root of the sugar-cane we observe, near the extremity, eight 

 larger vessels, distinguishable, in a transverse section, by their size ; 

 towards the exterior, several others of less diameter are visible, but in 

 this situation not well defined. At the distance of about a line from 

 the radicular^ extremity, the number of the larger vessels is nine ; at 

 about five inches there are ten ; and at the base of a root twelve inches 

 long, they amounted to twelve. On a successful section of the extre- 

 mity of the root being made, which should not only divide it into two 

 equal parts, but should also touch upon one of the eight larger vessels, 

 no difficulty will be found in recognizing upon the section, the origin 

 and successive development of these parts. It may then be observed 

 that the vessels become contracted, by insensible degrees, towards the 

 extremity of the root ; but that at the same time the cells of which 

 they are composed, become shorter and shorter, until their width is 

 more than double their length ; from which point, their transverse dia- 

 meter rapidly diminishes, and finally their dimensions, in either direc- 

 tion, are nearly equal ; and they have now become so small, that they 

 can no longer be distinguished from the adjacent cells. 



The extremities of the vessels, however, are not found, as might be 

 supposed, at the very extremity of the root, but are situated a short dis- 

 tance from it ; and, what is more curious, the extremities of all the 

 vessels converge to one point, to reach which they are bent consider- 

 ably. Moreover, as the rest of the cells composing the tissue of the 

 radicular extremity, and which, like those of the vessels, are disposed in 

 linear series, also converge to the same point, it is to be understood, 

 that not only the vascular, but also the cellular formation of the root 

 commences in, or starts from this point, which may with some reason be 



