ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
139 
Twisting* * * § of Filaments.* — Herr I. Robinsohn calls attention to the 
peculiar torsion of the filaments of some of the stamens in some Labia- 
tiflorae (Labiatae, Scrophulariaceae, Acanthaceae) and Irideae ( Gladiolus ). 
This appears to be connected with contrivances for pollination. In 
Digitalis , e.g., the two shorter filaments are quite straight, while the two 
longer ones are twisted in their lower part, the effect of the torsion 
being to bring the anthers of the longer filaments into a position imme- 
diately above those of the shorter filaments, where the pollen will be 
carried away by the visiting insects from the proterandrous anthers 
while the stigmas in the same flower are still closed. 
Elongation of the Axis.f — Herr E. Ule describes the remarkable 
elongation of the flower-stalk after flowering which takes place in a 
Brazilian orchid, Wullschlaegelia Ulei, but only if the flower has been 
fertilised. The purpose of the growth appears to be the dissemination 
of the seeds. Similar elongations of the flowering axis occur also in 
CJievreulia acuminata (Composite) and TJtricularia nelumbifolia. 
Xerophilous Plants. J— Herr Grevillius has studied the character- 
istics of the xerophilous vegetation of the Swedish island of Oeland. 
The most prominent are a csespitose habit, shoots or rosettes of leaves 
growing closely adpressed to the soil, and the great thickness of the 
leaves in proportion to their surface. Protection against excessive 
transpiration is afforded by a clothing of hairs, a covering of wax, or the 
thickening of the cuticle. The mechanical tissue in the lamina of the 
leaves is either feebly developed or entirely wanting. The internodes 
of the stem are generally shorter. 
Leaves of Xerophilous Plants. § — Herr B. Jonsson describes a 
peculiar form of leaf characteristic of certain tropical xerophilous 
genera, consisting in a great reduction of the assimilating tissue and a 
great development of tbe system for protection against transpiration. 
The palisade-parencliyme consists of a single layer of cells ; the chloro- 
plasts are usually few, but of large size ; the upper half of each cell is 
usually destitute of chlorophyll-grains, and often contains a cluster of 
crystals of calcium oxalate. This peculiar position of the chlorophyll- 
grains does not change with the varying direction of the light, and is 
apparently connected with the storing up of acids in the aquiferous 
tissue which lies above this layer. 
Structure and Function of Stomates.||— Herr H. C. Schellenberg 
classifies stomates under two types, viz. : — (1) The Amaryllis- type, in 
which each guard-cell may be regarded as a sac with two thickening- 
bands on one side only of the opening ; (2) the IZeZZe&orMS-type, in 
which the cavity of the guard-cell presents, on transverse section, an 
inequilateral obtuse-angled triangle. 
As concerns their function, the author regards stomates as assisting 
in assimilation, in transpiration, and in the interchange of gases, the 
* Oesterr. Bot. Zeitsclir., xlvi. (1890) pp. 393-401 (1 pi.). 
f Ber. Deutsch. Bot. Gesell., xiv. (1896) pp. 255-60 (1 fig.). 
% Engler’s Bot. Jahrb., xxiii. (1896). See Bot. Centralbl., lxviii. (1896) p. 223. 
§ Acta Univ. Lund, xxxii. (1896) 20 pp. and 2 pis. See Bot. Centralbl., lxviii. 
(1896) p. 324. 
11 Bot. Ztg., liv. (1896) l ,e Abtheil., pp. 169-85 (1 pi.). 
