IO 
F. Cavers. 
Many interesting contributions to the physiology and ecology 
of Sphagnum are to be found in the papers of Peterfi (28), Sernander 
(46), and Timm (47), besides those of Oltmanns and Paul which 
have already been referred to ; the earlier literature of the subject 
is given fairly fully by Paul in his 1908 paper. The writer has 
recently (4) given a summary of some of the more striking features 
in the biology and ecology of Sphagnum. 
Since the sexual organs and sporogonium are practically 
uniform in the various species, the classification of Sphagnum is 
based entirely upon the vegetative organs, and it is at any rate easy 
to divide the genus into a small number of fairly natural groups, 
but beyond this point there is no general agreement among sphag- 
nologists, some of whom have carried on controversies quite as 
spirited and even violent as those which have enlivened the history 
of lichenology ; perhaps the best—or worst—instance is to be found 
in the wrangle between Roll and Russow regarding the constancy 
of species in the genus Sphagnum, in the course of which Roll called 
Russow “ einen hartgesottenen verbohrten Art-Dogmatiker von der 
schlimmsten Sorte,” and even worse things. 
Apart from these somewhat barren and too often polemical 
discussions, it is generally admitted that the species of Sphagnum 
vary considerably, also that the different sections into which the 
genus has been divided show analogous variations. As was clearly 
pointed out by Jensen (8), the variations in the form of the Sphagna 
may be attributed to differences in the environmental conditions 
with regard to moisture, light, temperature, etc. The leaves are, 
naturally, the organs most liable to undergo variation, but the 
branching is also affected by these different conditions. Jensen 
distinguished three chief types of “ analogous variation ” :—(i.) 
“formas immersae,” growing submerged in water, with long stems, 
no distinct terminal head—the branch-tufts being widely separated 
owing to elongation of the stem—and with long leaves, the stem- 
leaves being similar in structure to the branch-leaves ; (ii.) “formse 
compacts,” growing in dry or cold habitats, in which the shoots 
are compact, forming low cushions, the branches short, and the 
leaves closely overlapping ; (iii.) “ formas squarrosae,” growing in 
sheltered and shaded places, with robust shoots, leaves broad and 
deep green in colour. Other types are “ laxae,” with the leaves 
widely spaced out; “ tenellae,” with unusually long and slender 
branches and narrow leaves ; “ falcatae,” with falcate arrangement 
of the leaves at the curved tips of the branches. Jensen pointed 
