238 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(3) The Mnlum- type ; a parenchyme differentiated into a uniform cen- 
tral cylinder and a chlorophyllous parenchyme ; (4) The Polytrichum- 
type ; a central cylinder differentiated into a medullary band and a 
pericyclic zone. In some stems with central cylinder there are indica- 
tions of branching. The epiderm of the underground stem is character- 
ized by the presence of absorbing hairs, that of the aerial stem by the 
existence of an external cuticle and by the internal cutinizatiou of the 
cell-walls. In the underground stem the cortical parenchyme always 
comprises a small number of layers, while the central cylinder is well 
developed ; in the aerial stem, on the other hand, the cortex is more 
developed, and the central cylinder greatly reduced. 
When an aerial moss is placed under aquatic conditions, the 
characters of the epidermal layer of the stem and those of the leaf 
undergo great modification. The epidermal cells increase in size, lose 
their cuticle ; the cell-wall is composed of cellulose only, and is greatly 
reduced in thickness ; changes also take place in the leaf. 
If mosses are cultivated in the air or in water, and the conditions of 
illumination and of the position of the stem are varied, the stems aro 
seen to be endowed with very feeble negative geotropic, and with strong 
positive heliotropic properties. The heliotropism is always prepon- 
derant, and the stems always direct their growth towards the source of 
light, whatever its direction. In a moist air the leaves oi certain 
mosses take two positions on the stem ; — one when the air is nearly 
saturated with moisture, the other when the air is comparatively dry; 
the latter is the closed position or that of sleep. The movements of the 
leaf from one of these positions to the other depend on the contraction 
or turgor of its chlorophyll-tissues. 
In both states of the leaf mosses disengage carbon dioxide in the dark, 
but the process is less active in the sleep condition ; and this is also 
true of the process of assimilation. The relation of the volume of 
carbon dioxide disengaged to that of oxygen absorbed is constant and 
normal. It is in the spring and the autumn, when mosses are moistest, 
that their vital functions are most active, and that the sexual oi’gans and 
sporogones are formed. 
Rabenhorst’s Cryptogamic Flora of Germany (Musci). — In Parts 
17 and 18 of this publication, the description of the Funariaceae is com- 
pleted, and that of the Bryaceae commenced. In this family the genus 
Mielichhoferia is first separated as a distinct group characterized by its 
lateral inflorescence and fruit. The remaining genera, comprising the 
group Bryeae, are Leptobryum, Anomobryum, Plagiobryum, Webera 
(20 sp.), Minobryum, Stableria, and Bryum. Of the latter genus, the 
subgenus Cladodium is alone included in these parts, itself including 
47 European species. The woodcuts are of the usual excellence, the 
structure of the peristome being especially elucidated in the species 
illustrated. 
Algae. 
Engler and Prantl’s Natural Families of Plants (Algae). — Of this 
important work four parts have now been published relating to Algae, 
viz. Parts 40, 41, 46, and 60, including the Conjugatae, Chloro- 
phycere, and Characeae, worked out by Prof. N. Wille, and the 
