Meyen's Report for 1839 on Physiological Botany. 331 



close-pressed lines, like streaks. It is now thirty years, says 

 M. Mirbel, since I first observed these streaks. On lon- 

 gitudinal sections these streaks appear vertical, and never 

 cross each other at right angles. Some years ago M. Mirbel 

 described an analogous case, namely, in the milk-vessels of 

 Nerium Oleander — [these vessels are the cells of the liber, and 

 in the Apocynece there is found in company with these another 

 quite independent vascular system which constitutes the true 

 milk-vessels! — Meyen], but the cause of the difference ap- 

 peared to him to be evident. Very fine granules, placed like 

 the squares on a chess-board, have the appearance of hori- 

 zontal, vertical, or even diagonal lines, according to the point 

 from which they are viewed. 



In other vessels M. Mirbel could not see these points, but 

 is inclined to believe, until a better explanation be given, that 

 these horizontal, vertical, and diagonal lines on the cells and 

 on the long and short utriculi, as well as in other vessels, are 

 caused by a quantity of undistinguishable papillae placed like 

 chess-board squares. [This preferable explanation, I believe, 

 was given by myself several years ago. — M.] 



From the hollow granulations up to the cells with thin, dry, 

 and striated sides, the vegetable matter forms one and the same 

 completely continuous cellular tissue, the contents of which 

 are modified by the advances of vegetation. The two states, 

 one of which M. Mirbel designates as that of continuous cel- 

 lular tissue, the other as a collection of distinct cells which 

 are either separated or combined solely by juxtaposition, de- 

 termine or fix two periods of utricular formation which may 

 be exactly distinguished. 



The root of the date-palm exhibits three clearly distinct or- 

 ganic regions, a peripherical, a medial, and a central. 



In the above-mentioned early stages of vegetation there is a 

 layer of cambium lying between the peripherical and the me- 

 dial part, as also between the medial and the central ; more- 

 over, there are in each region certain parts destined for the 

 formation of cells. 



The peripherical part being exposed to external injuries 

 would soon be destroyed if new cells were not added from 

 the neighbouring layer of cambium; this addition is the 

 more necessary, as the above-mentioned spots destined for 

 utricular formation are here wanting, and when the layer of 

 cambium is wanting this part of the root is reduced to two 

 or three layers of torn and lifeless cells. The medial re- 

 gion exhibits in its centre the oldest cells; the younger 

 they are the nearer they lie to the cambium of the outer or 

 inner region. Even if it should at first sight appear as if 



