4 — 
under the microscope one will see directly the reason for the different macroscopic 
appearance, in that those of 5 . ripariwn present a very concave enlarged basal 
part with relatively small, narrow, sharp-pointed tip in which the hyaline cells 
are suppressed, while in S. recurvum the leaves are quite lanceolate with undif- 
ferentiated tip. Even the pores show a decided difference, particularly in the 
middle and lower side-regions, where the hyaline cells in S. riparium have numer- 
ous pores much as in S. teres and 5 . squarrosum, this with other points of simi- 
larity suggesting a convergence of the two series Squarrosa and Cuspidata in the 
species S. teres and 5 . riparium . The stem-leaves show further a perfectly clear 
difference in that those of S. riparium are considerably larger than those of S. 
recurvum (averaging about i.6 X 1.2 mm. as compared with i X .8 mm.), and 
the characteristic rent of the former is entirely lacking in the latter. The two 
species do not in any way intergrade with each other so far as I know, though 
the next species, 5 . obtusum, is quite intermediate between them. The perichaetial 
leaves of S. riparium differ from those of all the species hitherto discussed in 
being made up entirely of homogeneous narrow cells with pitted walls; the cap- 
sule is relatively small as compared with the customary robustness of the plant. 
The species is perhaps rather more a s^amp plant than S. Lindbergii , but 
is similarly one of the far north. It is not uncommon in Greenland, Labrador, 
and Alaska and might be looked for almost anywhere in British America; in the 
United States it has not been found elsewhere than in the White Mountains of 
New Hampshire, where Faxon collected it. (Nos. 86 and 87 of the Eaton and 
Faxon exsiccata are from Crawfords.) It is, however, not impossible that it 
may be found elsewhere in the northern tier of states. In Europe it extends 
southward to the Alps and it is reported from several stations in northern Asia. 1 
15. Sphagnum obtusum Warnstorf, 1877. This species first recognized 
(though not ac that time well described or clearly understood) by Warnstorf 
has become fairly well established, but its detection still presents difficulties. Its 
outward appearance is much that of S. recurvum , from which I would not under- 
take to distinguish it in the field. In the course of microscopic examination 
one may be led to suspect its identity by the lack of the rather large round pores 
usually found on the inner surface of the branch-leaves of 5 . recurvum. The 
conclusive test which we owe to Limpricht 2 involves the use of a stain. Since 
Russow the staining of Sphagnum for the demonstration of the leaf-pores has 
been rather insisted upon. As a rule I do not regard it as necessary and think 
that most pores can be made out as well if not better without it, though it may 
at times be of advantage as a check upon results. I have used for the purpose 
the stock laboratory solution of methylene blue in preference to the violet stain 
generally employed for Sphagnum. For the certain detection of S. obtusum the 
use of some stain appears indispensable. So stained the branch-leaves under 
high magnification show small round white spots on the membrane of certain 
of the hyaline cells, which I have referred to 3 as “membrane-thinnings” because 
1 Cf. Jensen, Musci Asiae borealis, III, 146 1909. 
2 Rabenhorst Kryptogamenflora, IV, 1, 132. 1885, Cf. also Russow, Sphagnologisehe 
Studien, 103. 1819. 
3 North American Flora, XV, 15. 1913. 
