444 THURSTON: SEX IN THE CONJUGATAE 
cells, and nothing startling in considering the conjugation in all 
the species of the Mesocarpeae as fecundation. Even a case such 
as that described by Petit (4) for S. mirabilis, where he says that 
the contents of a single cell separate into two parts which reunite 
forming a spore, might be considered as a fertilization. There 
may also be an explanation here for many of the so-called aplano- 
spores and parthenospores, which when the facts are fully known 
may be found to go through some process similar to that described 
by Petit for Spirogyra or by Woodruff for Paramoecium. 
My purpose in gathering together the subtended tables has been 
to show the relative frequency of the different types of conjugation 
as shown in the literature. It is obvious that lateral conjugation 
is very common. This fact, together with occasional observations 
of cross conjugation, and the fact that both lateral and scalariform 
conjugation are often found not only in the same species, but in 
one and the same filament, go to prove that the individual cell 
rather than the filament should be regarded as the unit when the 
fusions in these forms are being considered. It is of course quite 
impossible in the present state of our knowledge to estimate 
finally the validity of many of these species. No claim is made for 
the completeness of the tables nor that all synonyms have been 
eliminated. In my opinion, however, they show approximately 
the proportions in which the different types of conjugation have 
so far been described in the literature and may be useful to students 
of the general problems of sex. 
The principal sources of the tables are such standard works 
as Wolle, Hassall, Cooke, Petit, De Toni, West and Collins (as 
indicated in parentheses), although numerous shorter papers have 
also been consulted. Acknowledgment is due Dr. R. A. Harper 
for suggestions leading to the compilation of the tables. Species 
which do not appear are omitted because no drawing or definite 
statement as to the method of conjugation could be found in the 
literature. 
TABLE I 
CONJUGATION SCALARIFORM, SPORE IN ONE OF THE CELLS 
Zygnema _ (Hassall) Zygnema cylindricum (Transeau) 
nomalum (Wolle) cruciatum (Wolle) 
oe 
és 
chalvbeieketwiens (West) 2 cyanospermum (Cleve) 
Collinsianum (Transeau) pe ericetorum (West) 

