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Amblystegium filicinum not infrequently grows in water, A. varium 
typically grows in wet places. The plants when aquatic are usually 
dark to blackish green and have a very stout percurrent costa and in 
some species paraphyllia are present. When aquatic the members of this 
subgenus are found on stones in brooks and springs. The leaf cells are 
typically very broad and short, 2-4: 1, much longer in large forms of A. 
fiuviatile and A. irriguum approaching respectively A. noterophilum and 
A. irriguum var. spinifolium, and in those forms themselves. 
It is in this group that the greatest difficulties are met as the species 
vary greatly and undoubtedly intergrade. A. fiuviatile forma typica 
Boulay is exactly illustrated by the plate (567) of the Bryologia Europea, 
except possibly that the costa usually appears stronger at the apex. The 
leaves are oblong to ovate-oblong, gradually narrowed to a rather blunt 
point; costa exceedingly stout and percurrent, nearly as wide at apex as at 
base; the upper leaf cells are elongated (for the group) and thick walled, in 
the lower 1/5 of the leaf broader and subrectangular. A. fiuviatile forma 
brevifolia Boulay, which is more like the form figured by Cardot as the type 
(See fig. 4) has shorter leaves, oblong-ovate to ovate, with fewer lax cells 
at base and these often brown, with very thick walls, becoming opaque 
with age. 
Through forma brevifiolia, fiuviatile grades into what I, in common 
with several authors both European and American, think to be the true 
orthocladon of Palisot (not of many other authors). In this the leaves are 
cordate-ovate, shortly and rather bluntly acuminate, with very short thick 
walled cells (2-3 : 1) with a few larger thick walled brown and opaque cells at 
the base in fully developed leaves. This I find to be not uncommon in the 
brooks of the East. A. irriguum (Wils.) B. & S. has forms which come 
very close to orthocladon but in general most of our forms have ovate- 
lanceolate, longly acuminate leaves with costa more tapering to the nar- 
rower apex. Amblystegium irriguum also has larger laxer floating forms 
which are to the commoner form what forma typica is to forma brevifolia 
in A. fiuviatile. Such in particular are plants collected by M. Dupret 
“ On stones in bed of a spring” Seminary of Philosophy” Montreal. 
This form of Amblystegium irriguum approaches the var. spinifolium 
and has the large elongated cells and laxer basal areolation of that variety. 
In the Montreal plants, at least, paraphyllia were so numerous that at first I 
thought it a form of A. filicinum , and indeed these two species also seem to 
intergrade so that the inflorescense alone will decide the relationship of some 
forms; if indeed this is ever decisive in the Hypnaceae. 
A. irriguum also appears to grade into varium , which typically is a less 
aquatic plant with more short cells at the marginal base of the leaf; leaves 
more ovate at base, more contacted to the insertion and more abruptly 
acuminate with a much more slender costa. The harshness and rigidity 
attributed to irriguum I have been unable to verify as a specific character, 
for most species of the group are harsh and more or less gritty. A. 
irriguum vox. flacidum De Not. is an attenuate floating form with very dis- 
tant and small leaves. 
