—82— 



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 off. 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- 



