ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
473 
ness, this being chiefly due to an increase in the elements of the sieve- 
portion of the vascular bundles. 
Swellings on the Leaf-stalk of Atragene.* — Herr W. Tonkoff 
describes the structure of the swellings which are found on the concave 
side of the leaf-stalk of Atragene alpina , at the spots where it curves 
in consequence of contact with a support. They differ from similar 
swellings on the tendrils of Ampelopsis in being rich in chlorophyll, in 
the cell- walls being thickened and lignified, and in their not forming a 
viscid exudation. 
Aerial Roots of Orchideae.f — Herr E. P. Meinecke has examined 
the structure of the aerial roots in a large number of genera of Orchidese 
belonging to a number of different tribes. 
The velamen is composed of a very variable number of layers of 
cells ; their walls are almost always strongly thickened ; the most 
common form of thickening is spiral, though the pitted and reticulate 
also occur ; the wall which bounds the endoderm is usually furnished with 
peculiar ridges ; and these are in places provided with the characteristic 
rod-like bodies. The endoderm forms a cylinder composed alternately 
of longer and shorter cells, the former having thicker walls than the 
latter. The development of the cortical parenchyme varies greatly ; its 
walls are usually very strongly thickened, and its mucilage is usually 
infested with fungus-hyphse, which penetrate also to the smaller 
endoderm-cells. The projecting sheath and the pericambium each con- 
sists of a single layer of cells. The degree of lignification of the vascular 
bundles is very variable. 
As a general rule the variations in the anatomical structure of the 
aerial roots correspond with the accepted limitations of the various tribes 
of Orchidese. 
Root of Parasitic Loranthaceae.f — According to M. P. Yan 
Tieghem. the root of some parasitic Loranthacese presents two remark- 
able peculiarities not found elsewhere in the root, — the entire absence, 
in the cortex, of a framework to the endoderm, and the presence, in the 
stele, of fibrous pericyclic bundles outside the phloem-bundles. The 
greater number of parasitic Loranthacem are entirely destitute of roots ; 
but in others adventitious roots of endogenous origin are produced either 
at the base of the stem only, or along the internodes, or at the nodes. 
The peculiar structure described was found in the lateral aerial roots of 
species belonging to six genera, Macrosolen, Oryctanthus, Loranthus , 
PJirygilanihus, Phihirusa , and Struihanthus. Similar modifications of 
the primary structure have long been known in the stem and leaf. 
3 . Physiology. 
Cl) Reproduction and Embryology. 
Chromatophily of the Huclei of the Embryo-sac.§ — From an 
examination of the embryo-sac of a number of plants (chiefly Monocoty- 
ledons) M. M. Raciborski states that in all the Angiosperms examined, 
* Ber. Deutsch. Bot. Gesell., xii. (1894) pp. 40-8 (1 ph). 
t Flora, lxxviii. (1894) pp. 133-203 (2 pis.). 
| Bull. Soc. Bot. France, xli. (1894) pp. 121-7. 
§ Anzeig. Akad. Wiss. Krakau, 1893. See Bot. Centralbl., 1894, Beih., p. 24. 
