1906] LEWIS—DEVELOPMENT OF RICCIA ars 
cultures in the laboratory the forms have been observed showing 
the transition. There can be no doubt that the plant which I have 
described is the true Ricciocarpus natans, and the description of 
the ground form as a distinct species came about naturally from 
the conditions of its growth. In such ponds as have been observed 
here, the water is high in April and May, so that the floating plants 
are carried up around the edge and left on the soil. In June or 
July the water has entirely disappeared from the pond and the only 
plants found are the slender ribbon-shaped ones which have developed 
from the floating form. In my first summer’s collecting, when 
the ponds were dry by the last of June, I saw not a vestige of the 
old Ricciocarpus natans, and felt sure that the plants collected were 
Riccia lutescens. It seems possible that the plant was first described 
as a distinct species from material collected under similar conditions, 
because it is said to occur in dried up ponds and ditches. If in 
summer and autumn some water were present, so that some of the 
typical Ricciocarpus natans would be found floating, the origin of 
the ground form might readily be seen, but in such a case there 
might be failure to associate the ground form with Riccia lutescens. 
Only by following the development and observing the transition of 
one form into the other under different conditions of growth can 
the true relationship be determined. My observations have con- 
vinced me that Riccia lutescens is only a ground form of Ricciocar pus 
natans and should not be regarded as a distinct species.’ 
The plant now known as Ricciocarpus natans was formerly 
‘regarded as a Riccia. In the structure of the thallus Ricciocarpus 
is more complicated than the species of Riccia. The most important 
taxonomic characters, however, have been the arrangement of the 
sexual organs and structure of the sporophyte. 
Hooker first found fruiting plants in dry specimens sent to him 
by Torrey from New York in 1824. BrscHorr found fruiting 
plants in the autumn of 1829 near Heidelberg, and describes anthe- 
ridial plants, but his figure of the antheridium is not very convincing, 
? Having determined the ground form as Riccia lutescens, specimens were sent to 
Professor A. W. EVANS in October 1904. He considered that we were right in refer- 
ring the plants to that species, but stated the views of different authorities in regard 
to the status of the species. 
