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Evidence is first presented to show that an aquatic form of Riccia is not nec- 
essarily sterile, even in Europe. In old specimens collected by A. Braun at 
Tempelhof near Berlin and labeled by him R. "fluitansfructifera" archegonia 
are present in abundance. These specimens lack rhizoids and present every 
appearance of having been aquatic in habit. Wherever archegonia are situated 
the thallus is distinctly broader, and where the archegonia are separated from 
one another by sterile tracts the thallus shows a series of marginal lobes on each 
side, indicating the position of the archegonia. Von Gaisberg compares the 
Tempelhof Riccia with the African R. Dinteri Steph. (apparently a manuscript 
species), which was found on stones in a spring. Here too the position of the 
archegonia is marked by marginal lobes. Unfortunately he gives us no data 
regarding the spores in either case. It should be mentioned in this connection 
that Familler (2, p. i66) had already noted the occurence of fruit in the aquatic 
form of " R.fluitans" , before he had developed his later ideas regarding the species. 
His specimens came from Bavaria, but he tells us nothing about their structural 
features. 
In his experimental work Von Gaisberg first utilized an aquatic form of " R. 
Jiuitans" growing in the university greenhouse at Munich. When this was 
transferred to soil it gave rise to what he called a "broad form," but even in this 
condition remained perfectly sterile, so that it was impossible to assign it to any 
known species on the basis of characters derived from the spores. He then turned 
his attention to an aquatic Riccia which he found in the vicinity of Starnberg 
in Bavaria. This plant was determined by Familler, presumably on the basis 
of its morphological features, as R. Huebeneriana; but when it was cultivated 
on soil it gave rise to a "broad form" essentially like that derived from the 
greenhouse material. Von Gaisberg expresses the opinion that this "broad 
form " is distinct from "R.fluitans f. canaliculata " and also from R. Huebeneriana. 
Although he thus differs. from Familler, so far as the latter 's determination of 
the Starnberg material is concerned, he agrees with him in considering " R. 
fluitans" a composite species and cites, in further defense of this view, the wide 
variation in width exhibited by herbarium specimens bearing this name. 
In the brief description of the "broad form " it is noted that the air chambers 
are more or less polygonal; in cross section the thallus is bounded on each side 
by a single large chamber but elsewhere the chambers appear to be in two layers 
or sometimes, in the median portion, in three. Although these features might 
serve to distinguish the plant from R. Huebeneriana, as this species is usually 
described, they would hardly distinguish it from the "forma canaliculata" ; 
and it is unfortunate that no other differential characters are indicated. 
The work here reviewed shows that our knowledge concerning " R. fliiitans'' 
and certain terrestrial forms or species of the subgenus Ricciella is still far from 
complete. It shows further that additional culture experiments and accurate 
morphological comparisons will be necessary before satisfactory conclusions 
can be reached. The species of this subgenus are exceedingly variable and react 
to slight environmental differences. R. Huebeneriana, for example, although 
seemingly very distinct from R. pseudo-Frostii in size, in color and in the shape 
