Recent Work on the Bryophyta. 273 
curved and sickle-shaped (falcato-secund) leaves; sheathing leaf- 
bases ; papillae and mamillae—solid and hollow outgrowths res¬ 
pectively of the leaf-cells; water-storing tissue in the leaves; thick- 
walled leaf-cells; increase in number of layers in the lamina to two 
or more ; strengthening of the leaf-margin by increase in number 
of cell-layers ; development of lamellae and other outgrowths on 
the surface of the leaf; undulation, wrinkling, and folding of the 
leaf; presence of paraphylls and dense rhizoid-covering on the stem; 
hygroscopic movements of the leaves, and so on. 
Space does not permit detailed notices of a number of recent 
floristic works on Bryophyta which are of interest on account of the 
greater attention which is now being paid by systematic writers to 
observations on the biology and ecology of these plants. Increasing 
numbers of systematic bryologists are bringing to bear upon the 
problems of relationship the results of recent microscopic and 
physiological work, and realising the importance of studying 
bryophytes season after season in the field in order to observe the 
influence of changing conditions of light and moisture and other 
factors on the morphology of these plants. On the other hand, 
workers in Ecology are realising, to a greater extent than formerly, 
the important part played by bryophytes as dominant, associate, or 
pioneer plants in the vegetation of arctic-alpine, cliff, heath and 
moorland formations. 
The ecological importance of the genus Sphagnum has, as 
might be expected from the conspicuous role played by these 
mosses in heath and moorland bogs, given rise to a considerable 
literature. During the last few years new ground has been broken 
as the result of biochemical researches on peat and the peat-mosses 
(Sphagnaceae), opening up a line of work which has already yielded 
important results. The first detailed work in this direction was 
that of Czapek (Flora, Band 86, 1899), who found that the cell-walls 
of Sphagnum and other aquatic mosses contain an antiseptic phenol¬ 
like substance which he named “ sphagnol,” also that the membranes 
in Sphagnum are rich in pectic bodies. In two papers devoted to 
the question of the calciphobous character of Sphagnum, Paul (29, 
30) found that not all salts of calcium have an equally injurious 
effect; that the most injurious are the alkaline salts of this metal, 
e.g. calcium carbonate,and of potassium and sodium, and free alkalis; 
that the peat-mosses give an acid reaction, suggesting that the 
injurious effect of calcium carbonate is perhaps due to the 
neutralisation of the acid ; that, as Gully had shown, high-moor 
species contain more acid than low-moor species, the former being 
more sensitive to lime; that on high moors there is less mineral 
food available in the substratum for the Sphagna and the plants 
take more food from the air, the acids probably playing an important 
part in this process; that the amount of acid and the degree of 
sensitiveness to their neutralisation decrease as the amount of 
available mineral food increases. The more recent work of 
Baumann and Gully (2) has overthrown the old views concerning 
the existence of free “ humic acids ” in peat and the peat-mosses, 
and has shown that the acid reaction of peat and of living Sphagnum 
plants is due not to true acids but to colloidal substances of acid 
character which are present in the walls of the hyaline leaf-cells, 
and are doubtless identical with the pectin-like substances extracted 
