ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
519 
of much shorter cells then the central bundle, resembling bast-cells in 
their form ; they do not give a definite cellulose reaction ; they contain 
tannin, especially in the spring. The epiderm consists of a single layer 
of cells, at all events in the upper part of the stem ; later it divides by 
tangential walls. The cells of the cortical tissue are connected with 
one another by means of pits which often can only be detected by the 
use of staining reagents. They are much more obvious in P. juniperi- 
num. The central bundle must be regarded as a rudimentary vascular- 
bundle-system ; but its function is much more that of storing up and 
conducting food-material than of the simple conduction of water. Its 
collenchymatous character indicates also that it may serve as a reservoir 
of water. 
The biserial and dorsiventral arrangement of the branches (in 
Hypnum splendens ) does not depend on anatomical considerations or on 
inner causes of growth ; both this peculiarity and the horizontal position 
of the branches are due to constant illumination on one side only ; geo- 
tropism alone, without the co-operation of light, causes the shoot to 
ascend vertically. 
Stem-leaves of Sphagnum.* — Dr. F. OrtlofF publishes, in a card- 
board box, 66 photomicrographic representations of the stem-leaves of 
bog-mosses. Except in a few instances, the form, size, and arrangement 
of the cells of the leaves are clearly shown, as well as the thickness of 
the cell-walls, and the difference exhibited in these points by the different 
species and sub-species, of which 54 are delineated. The scale of 
magnification is uniformly 100. 
Alg-ae. 
Increase in Thickness of the Floridese.t — Herr B. Jonsson calls 
attention to the concentric rings of tissue, similar to those of Lami- 
naria ;, in the Florideae. They are especially well developed in Ahnfellia 
plicata and Phyllophora membrani folia, but occur also in other red 
sea-weeds. In the young apex of a shoot of Ahnfeltia the central 
string of tissue is surrounded by a chlorophyllous cortical layer, while 
in older parts the cortical layer is differentiated into a number of 
distinct rings, sometimes as many as twelve, which may be either concen- 
tric or excentric ; two adjacent riugs are usually separated by a single row 
of thick-walled cells. The inner portion of each zone is of a lighter 
colour than the outer portion ; and the rings themselves change from 
within outwards, from grey-green to an intense red. This structure is 
undoubtedly due to a periodicity of growth ; though on what causes this 
periodicity depends is obscure. The lighter colour of the inner portions 
is attributed by the author to the interruption of the light due to the 
activity of growth which immediately follows the re-awakening of 
vegetation. The structure appears to be a contrivance for increasing 
the flexibility of the plant. Similar phenomena occur also in Melanthalia 
abscissa , and in other seaweeds belonging to the Oryptonemiaceae, Gigar- 
tinaceae, Khodymeniaceae, Sphaerococcaceae, and Rhodomelaceae. 
* ‘ Die Stammblatter v. Sphagnum,’ 8 pp. and 66 pis., Coburg, 1891. 
t Lunds Univ. Arskr , xxvii. (1890, 91) 41 pp. and 2 pis. 
