522 BOTANICAL GAZETTE [FEBRUARY 
was the most favorable time for the collection of material showing 
karyokinesis in the spore mother-cells. During August, the spores 
became mature and the thalli broke down. No good specimens 
could be collected after August 25. This differs from what has 
been observed for some other species of Riccia, which are described 
as withstanding long periods of drought, the thalli continuing their 
growth again when supplied with moisture. (CAMPBELL, 3.) 
During the following winter this pond became filled with water 
and did not become dry until late in the summer, so that only a few 
plants were found as compared with the large number of the pre- 
ceding year. This made a difference in the time of fruiting. In 
September the sporophytes were in about the same stage of develop- 
ment as in July of the preceding year. This may explain why 
different authors give different seasons for the fruiting of Riccia. 
It seems that conditions of temperature and water supply exert such 
an influence that in the same species and locality the time may vary 
considerably from year to year. In general, I think it may be said 
that good conditions for vegetative growth will hasten rather than 
retard the fruiting of Riccia. 
The thallus of Riccia crystallina is small and thin; its surface 
presents a series of wide depressions separated by thin lamellae; 
and there are no ventral scales. The fixing fluid easily penetrates 
and the spore mother-cells are usually well fixed. 
The development of the spore mother-cells agrees with the account 
given for Riccia natans, but there is not such a large number produced 
in a sporogonium. When the spore mother-cells come to lie loosely 
in the sporogonium, they are surrounded by nutritive material. 
The mature spore mother-cells are then generally spherical, but 
they may be elliptical or so angular by crowding as to look like a 
tissue. The contents of the spore mother-cells of Riccia has been 
described as granular by CAMPBELL (3) but the structure of the 
cytoplasm in Riccia crystallina is a fine reticulum with the granules 
occurring usually at points of intersection of the fine threads of the 
network. The older spore mother-cells as well as the mature spores 
contain considerable oil. 
In the nucleus of the spore mother-cell the chromatin is scanty 
and is irregularly scattered on a fine linin network. No nucleolus 
