Meyen’s Report for 1839 on Physiological Botany. 333 
the interior, and between which a communication is esta- 
blished by means of openings. 
The central region of the root derives its utriculi from the 
inner layer of cambium, as do also the inner parts of the me- 
dial region. Here also the oldest cells lie in the middle, but 
are cylindrical, they are connected only in some points, and 
are in full vegetation. They soon, however, pass into the 
compound state. The youngest exterior cells are, as it were, 
only cellular cambium; at this age the central region can be 
clearly distinguished from the medial. Afterwards there is 
formed between them a plate or stratum of the thickness 
of a single layer, the cells of which assume a determinate 
form, either tetrahedral or in form of a parallelogram ; they are 
equal and closely connected together in concentric rows, while 
the tubes of the medial part have no fixed form. At a later 
period the cells of this zone become filled with cambium, 
which soon forms irregular tissue. They increase in size, al- 
ways retaining their concentric arrangement, and each is de- 
veloped in the form of a semicircle whose diameter lies on the 
medial region. In the centre of each of these semicircles there 
is a small cell analogous to the large containing cell. From 
its external surface proceed vertical partitions in different 
directions like rays, which are attached to the inner surface of 
the large cell. ‘The metamorphosis proceeds rapidly, and can- 
not be followed by the most attentive observation. 
The increase of the central region by the insinuation of new 
cells begins at a slight distance from the centre, and becomes 
continually greater till it reaches the above-mentioned zone. 
This phenomenon (one of the most curious in the whole 
formation of vegetable organs) “takes place in every cell 
by means of successive deposits of cambium, which ex- 
ists but a short time itself, but before it disappears produces 
a quantity of small cells which are often destined to live for 
centuries. Vessels of all sizes pass lengthwise through the 
central region ; the larger lie towards the centre, the smaller 
near the periphery; all are polyhedral tubes, whose sides are 
penetrated by transverse clefts (or at least apparently so), and 
have more or less the appearance of small ladders, and hence 
the name “ Vasa scalariformia” (Treppengefasse). In a note 
M. Mirbel adds, that he has found in the root of the date- 
palm that that which appears to be an opening is probably 
in most cases only a spot where the side of the cell is thin; 
but a thinning of the membrane is not very far from an 
opening, and every opening in a tube commences by it*. 
* The opinions concerning the pores which occur so frequently on the sides 
of cells have been very various. Their discoverers, Moldenhawer the elder, and 
