Meyen’s Report for 1839 on Physiglogical 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 Apocynee 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 papillz 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 
