ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
323 
Dr. J. Yan der Plancken and M. P. Biourge* * * § have collected the 
white drops which fell from three copper beeches. The drops were 
about the size of sand-grains, and when fairly well purified were found 
to be odourless and very hygroscopic. The honeydew was sweet, and 
stuck to the teeth like gum. It was very soluble in water and dilute 
alcohol, and the solution turned the plane of polarisation to the right. It 
did not contain nitrogenous matter, and when incinerated left 1 • 55 per 
cent, of ash composed of OaO, MgO, K 2 C0 3 . It is a mixture of gum, 
dextrin and levulose, and contains no saccharose. 
(3) Structure of Tissues. 
Protecting Tissues of Shrubby Plants.* — Herr P. Segerstedt de- 
scribes the contrivances for protection in the stem of a number of 
shrubby plants. The formation of periderm takes place earlier when 
the epiderm is not strongly cuticularised. The outer walls of the epi- 
dermal cells are thicker in inverse proportion to the development of the 
assimilating tissue. The formation of hairs is, as a general rule, of 
secondary importance. A red pigment is of frequent occurrence in the 
epiderm or in the hypodermal parenchyme. Tannin is most common in 
those species which have perennial branches that do not form periderm. 
The formation of cork is frequently determined by external conditions. 
Formation of Duramen.^ — M. E. Mer describes in detail the pro- 
cesses by which duramen or “ perfect wood ” is formed in a variety of trees, 
chiefly by the deposition of tannin and resinous substances. The dura- 
men does not always consist entirely of dead cells. The cause of the 
tannin entering the tissue is probably the decrease in turgidity of the 
vessels. f • ... .! 
Aerenchyme.§ — Mr. H. von Schrenk describes the modification which 
takes place in the tissue of many American plants when the stem is 
completely immersed in water, similar to that which has been observed 
in the trees of mangrove swamps. The species especially described are 
Lycopus sinuatus, Ludwigia spliserocarpa , and Sambucus canadensis. 
LacunaeCinithesTissue of Gymnosperms.|| — -Herr S. Rywosch has 
detected lacunae at the boundary of the protoxylem and parenchyme in 
the stem and leaf of many Gymnosperms (Coniferae and Ephedra ). 
These lacunae are not air-chambers, like those of water-plants, but 
appear to result from the inability of the annular and spiral elements to 
follow the expansion of the living elements which adjoin the protoxylem ; 
the lignified elements are forced apart, and the lacunae result. The 
best examples were seen in the leaves of Pinus austriaca and P. insignis. 
IntercellularlSpaces in Embryos.f — Mr. K. M. Wiegand describes 
examples of thisTrather rare phenomenon in the case of the embryo 
* La Cellule, xi. (1896) pp. 375-99. 
f Bih. K. Svensk. Yet. Akad. Handl., xix., 86 pp. and 3 pis. See Bot. Centralbl., 
lxv. (1896) p. 154. 
+ Bull. Soc. Bot. France, xlii. (1896) pp. 582-98. Cf. this Journal, 1888, p. 446. 
§ Proc. Amer. Micr. Soc., xvii. (1896) pp. 98-104 (3 pis.). 
l| SB. Naturf.-Gesell. Univ. Dorpat, x. pp. 515-7. See Bot. Centralbl., lxv. 
(1896) p. 70. T| Proc. Amer. Micr. Soc., xvii. (1896) pp. 174-6 (1 pi.). 
