132 BOTANICAL GAZETTE [FEBRUARY 
in other plants appear only in the last two generations of cells con- 
cerned in the formation of spermatozoids. 
Those who argue in favor of the homology of the centrosome 
and blepharoplast certainly find their best evidence so far in the 
liverworts, but it seems to me that this evidence is not conclusive 
when the bodies occur only in cells of the antheridium. 
In those plants in which centrosomes are known to occur, a single 
body divides to produce two, which arrange themselves on opposite 
sides of the nucleus (MoTTIER, 25). IKENO has reported a similar 
condition in Marchantia. In Riccia natans, however, the evidence 
seems to favor the view that the two bodies arise anew with each 
division, appearing on opposite sides of the nucleus at the same 
time. In this respect they behave more like blepharoplasts. 
MorrieR (26) in discussing this question has called attention 
to the fact that it is questionable whether we can speak of organs 
as homologous which, as such, are without genetic continuity. The 
question as to whether true centrosomes have genetic continuity 
has not yet been decided, but it is probable that they do not in all 
cases. 
| SUMMARY. 
1. Reccia lutescens and Ricciocarpus natans are forms of the same 
plant, the former occurring on the ground in summer and autumn 
when the ponds are dry, and the latter as a floating form. Either 
form can be changed into the other by altering the supply of water. 
Therefore, Riccia Jutescens should not be regarded as a distinct 
species. : 
2. The genus Ricciocarpus has been based largely on characters 
which do not exist. In my opinion, the only real basis for separating 
it from Riccia is the more complex structure of the thallus. BiscHOFF 
did not regard this as a good character for the separation of the genus. 
3. The plant is monoecious, antheridia and archegonia being 
produced in definite groups in the same thallus. The sexual organs 
appear in autumn when the thalli are growing on the ground and 
complete their development the following April. Abundance of 
water is not essential to sexual reproduction, as the plants fruit when 
kept growing on the soil and supplied with a limited amount of 
