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as an aquatic, unattached plant. At the same time several closely related species 
that grow on soft mud along the borders of ponds or streams, but not in the water 
itself, have been described. Two such species, R. Huebeneriana Lindenb. and 
R. pseudo-Frostii Schiffn., appear in recent European manuals; in North America 
R. Huebeneriana has likewise been reported, but R. pseudo-Frostii is replaced 
by R. Sullivantii Aust. Another more distantly related species, R. Frostii Aust., 
may be mentioned in this connection; this grows in similar localities and has 
a wide distribution on both sides of the Atlantic. 
Recently, especially in Europe, the opinion is becoming more and more 
widely held that some of these other species of Ricciella may live as aquatic 
plants too, giving rise to states or forms which resemble the aquatic form of 
" R. fluitans" in a marked degree. The advocates of this opinion hold that these 
various aquatic forms have been included in the old conception of " R. fluitans" 
and that the latter is, in consequence, not the aquatic form of a definite species 
but merely an aggregation of the aquatic forms of various distinct species. 
One of the earliest papers bearing on these points was published by Torka 
(7) in 1906 and dealt with R. Huebeneriana, which he discovered near Schwiebus 
in eastern Germany, growing as a terrestrial plant on mud. He placed some 
of this mud, which bore rosettes of the Riccia, in a glass receptacle and flooded 
it with water. After a while the tips of the thalli began to elongate and fork, 
but instead of clinging to the mud these new growths failed to develop rhizoids 
and often became detached, floating freely on the surface of the water. Here 
they remained green for some time but eventually perished unless the water 
was drawn ofT. If this was done the floating fragments would be left on the mud 
and would renew their growth, giving rise to attached plants of a fairly normal 
appearance. The part that had previously floated, however, failed to develop 
rhizoids and assumed a brownish color, apparently indicating a disintegration 
of the tissues. 
On the basis of these results^ Torka concluded that R. Huebeneriana would 
be able to maintain itself as an aquatic plant in the open, if the places where 
it grew were flooded. In his opinion floating plants of this character would be 
the only ones to survive the winter, attaching themselves to the substratum and 
developing normally after the water had sunk to its usual level in the spring. 
He thus ascribed to R. Huebeneriana an amphibious habit, comparable with 
that of R. fluitans. 
Five years later (8. p. 205) he announced the discovery of aquatic plants 
of R. Huebeneriana near Nakel and Zablocie in Poland and described them as a 
new variety under the name Ricciella Hubeneriana var. natans. In his description 
he notes the lack of rhizoids and the tendency of large mats of thalli to break 
up into small mats as the older parts die. As a result of this process the surface 
of the water becomes closely covered with innumerable plants in the late summer 
and early autumn. At the edge of the water some of these floating fragments 
attach themselves to decaying plants or to the moist earth, where they develop 
rhizoids as they continue their growth, showing a tendency to develop into a more 
robust terrestrial form, just as the floating fragments did in his culture experi- 
