THURSTON: SEX IN THE CONJUGATAE 443 
gametes as those of size and motility are perhaps to be considered 
as mere adaptations introduced in evolution to facilitate the 
bringing together of the twoelements. Tréndle (5), for example, 
claims to have proved that the vegetative cells of the Spirogyra 
filament are haploid; then the difference, in the case of Spirogyra 
at least, between somatic cells and gametes can not be one of 
chromosome number, but some difference there must be to inhibit 
further vegetative division in any given cell of a filament and 
cause instead a union of that cell with another which has under- 
gone a similar change. The gametic nature of any cell in a fila- 
ment would then be fixed when it ceases to have the power to 
divide but instead has a new found power to unite with some one 
of its fellows. At that moment the cell ceases to be a somatic 
cell and becomes a gamete. 
Cunningham (3) has reviewed the literature of the sexuality 
of Spirogyra rather thoroughly, but he throws out the cytological 
- evidence of Tréndle when he compares the filament of Spirogyra 
with the sporophyte of higher plants. He concludes that ‘reduction 
may occur in the zygote, in which case a filament wholly of one sex 
arises, or reduction may occur just previous to reproduction, in 
Which: Casey cs a es filaments of a bisexual nature are produced, 
which would conjugate either laterally or by cross-conjugation.”” 
Two of the species described by Tréndle as having the reduction 
take place in the zygote, would therefore according to Cunningham 
produce filaments ‘“‘wholly of one sex,’’ which however are known 
to conjugate in both the lateral and scalariform manners (see 
TABLES I and III). These are S. Jongata and S. neglecta. The 
real evidence of fecundation in these forms is not to be found in a 
visible or measurable difference between the filaments or even 
between the cells that fuse, nor is it to be found in the method 
of conjugation, whether lateral, scalariform, or cross conjugation, 
' but it lies in the newly achieved possibility of fusion itself with 
resultant doubling of the nuclear material and the subsequent 
reduction division, which as far as the evidence extends at present 
takes place on the germination of the zygospore. If we believe 
that similarity between gametes favors rather than hinders fusion, 
then there is nothing at all startling in considering lateral con- 
_ jugation as a fertilization even if the cells taking part are sister 
