ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
219 
formation of duramen begins about the middle of .July. It is distin- 
guished from the alburnum by the absence of starch, by the presence of 
thy Use, by an increase of substance of about 6 per cent., and by an 
increase in the specific gravity of the substance of which the cell-wall is 
composed from 1*55 to 1 * 59 ; the proportion of carbon has increased by 
about 1 per cent. The various tissues of the oak contain different 
tannins. The brown colour of the duramen is due to subsequent 
changes. 
Comparison of Duramen and Alburnum.* — From a series of experi- 
ments on the composition of the ash, Herr H. Zimmermann finds that 
the alburnum of trunks (chiefly elm) usually contains no lime, while 
large quantities of calcium carbonate are often stored up in the duramen. 
The largest quantity was found in the innermost rings of wood. 
Internal Pericycle. | — According to M. L. Flot the vascular portion 
of the inner pericycle does not originate on the inner margin of the 
procambium. On the inner side of the vascular bundle a larger or 
smaller portion of the procambium is retained, and this the author 
proposes to call the internal pericycle. It forms a continuous zone when 
the bundles are connected laterally ; while it is composed of distinct 
bands when they are free. Various kinds of tissue are regarded by the 
author as products of the inner pericycle : — long-celled parenchyme in 
the Crucifer®, Papaverace®, and Euphorbiace® ; lignified elements in 
many trees, also in some Composit® and Umbellifer® ; sieve-tube 
elements in the Apocynace®, Asclepiade®, Solanace®, (Enothere®, &c. ; 
a meristem, from which either sieve-tube or vascular bundles may sub- 
sequently be formed ; the bundle-sheath of Monocotyledons ; and a band 
of elongated cells uniting the bundles, in Achyranthes , Fagopyrum , 
Begonia, Labiat®, &c. 
Mucilage of the Membrane of Vegetative Organs.^ — Herr H. 
Walliczek has investigated the structure and origin of the mucilaginous 
epiderm of leaves, and classifies the various instances under three types, 
viz. : — (1) the lowermost wall of the epidermal cells is simply thickened 
by a secondary mucilaginous membrane ; (2) a layer of cellulose is 
subsequently deposited upon this mucilage (this has been misinterpreted 
as an epiderm composed of two layers of cells) ; (3) the upper and lower 
wall of certain epidermal cells are both thickened by a secondary muci- 
laginous membrane, on which is deposited a layer of cellulose, the lateral 
wall remaining unthickened; (4) an alternate deposition of mucilage 
and cellulose takes place on the wall of nearly all the epidermal cells. 
The mucilage is always formed as such, and is not the result of the 
transformation of other substances. 
In a large number of trees and shrubs, of which Tilia grandifolia 
may be taken as a type, mucilage cells occur in the interior of all the 
vegetative organs, the thickening-layers of which are subsequently for 
the greater part absorbed. The mucilage is never formed, as has been 
stated by some writers, within the protoplasts, but always on the 
boundary between the primary cell- wall and the protoplasm. Within 
* Zeitschr. f. angewandte Chemie, 1893, pp. 42G-30. See Bot. Centralbl., lvi. 
(1893) p. 37. t Comptes Rendus, cxvi. (1893) pp. 332-4. 
X Jahrb. f. wiss. Bot. (Pringaheim), xxv. (1893) pp. 209.-77 (3 pis.). 
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