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The Morphology of Riccia Fluitans L. 



Fred Donaghy. 



Since 1835 the Rieeias have received more or less attention by the botan- 

 ists. Bischoff, Lindenburg, Hoffmeister, Leibgeb, Garber, Lewis, Campbell, 

 Black and Atwell, have in turn made many valuable contributions to our 

 knowledge of this group. Still many problems of morphology and ecology 

 confronts us. Several species common to Indiana remain almost unstudied 

 as to detail. Among these none seem more interesting than the study of 

 R. fluitans. 



This species is widely distributed over the temperate zone and over 

 glaciated Indiana. Botanists recognize two forms, an aquatic and a terrestrial 

 type. The aquatic form is very abundant around Angola, Fort Wayne, 

 Logansport and Terre Haute. During the summer and autumn mats of 

 aquatic R. fluitans can be found floating in the ponds and sluggish streams. 

 In winter these mats sink to the bottom of the ponds and remain there till 

 spring. The continued cold does not seem to injure the plants which lie 

 below the ice, but those plants which are frozen in the ice are much winter- 

 killed, the apical ends alone remaining green. During the warm spring these 

 plants make rapid growth, and by summer patches of thalli again dot the 

 ponds and streams, showing that under favorable weather conditions the 

 thalli reproduce vegetatively very rapidly. 



Aquatic R. fluitans is sterile, branches dichotomously, the sprouts diverg- 

 ing widely, and often become recurved. The apical ends are deeply notched, 

 and truncate. Both dorsal and ventral surfaces bear chlorophyll. Rhizcids 

 and ventral scales are absent. 



When evaporation is excessive and the ponds are low, the narrow thalli 

 widen at their apical ends somewhat, and lose some of their characteristic 

 color. This is especially noticeable in those plants which grew in unshaded 

 ponds. The thalli which grew in ponds bordered by forest trees did not 

 show a marked change in width and color, due no doubt to the protection 

 afforded by the overhanging boughs and leaves. When single thalli are 

 washed ashore they generally die. More often, mats of plants are washed 

 upon the wet edges of the ponds. In favored places the thalli coming in con- 



