-85- 



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. "fluitans fructifera" 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. 166) 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. 

 fluitans" 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. fluitans" 

 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 



