1906] YAMANOUCHI—POLYSIPHONIA VIOLACEA 431 
describes what he has called a synaptic stage in the nucleus preceding 
the two mitoses concerned with oogensis in Plasmopara, and Trow 
holds that chromosome reduction takes place in the two mitoses in 
the oogonium of Achyla. These interpretations have been discussed 
and criticized by Davis (21, 23), and the suggestions of ROSENBERG 
and TRow do not seem to me convincing. 
Among algae, one of the best known accounts of gametogenesis is 
that of Fucus (STRASBURGER 73, FARMER and WILLIAMS 32), where, 
although spermatogenesis has not been investigated, the history of 
Cogenesis indicates a period of chromosome reduction. Conse- 
quently the fusion nucleus in the fertilized egg has the same number 
of chromosomes as the nucleus in the vegetative plants of Fucus, 
which led STRASBURGER (73, '75) to conclude that the Fucus plant 
is a sporophyte generation and that the gametophyte is so greatly 
teduced that it is only represented by single cells —male and female 
§ametes —before fertilization. 
Other examples among the thallophytes in which the life history 
has been worked out in some detail are Dictyota and Nemalion. 
In Dictyota (Wittrams 81) the fertilized egg nucleus gives rise to 
an asexual plant with double the number of chromosomes, and conse- 
quently a sporophytic generation. This asexual plant develops 
spores in groups of four accompanied by chromosome reduction, and 
these spores develop the gametophyte generation. This type of life 
history is clearly analogous to that of Polysiphonia. In Nemalion 
(WoLFE 86) the fusion nucleus of the fertilized carpogonium has a 
double number of chromosomes which appear in all of the cells of 
the cystocarp (sporophytic) up to the formation of carpospores, where 
the reduced number of the gametophyte is reported to appear. 
Wotrr’s account, however, does not give the details of this chromo- 
some reduction with the characteristic stage of synapsis followed by 
{Wo successive mitoses. 
Chromosome reduction in Polysiphonia is clearly similar to the 
Phenomena of sporogenesis in higher plants, and takes place at the 
time of tetraspore formation. The carpospores, containing the — 
phytic number of chromosomes, continue the sporophyte generation by 
developing the tetrasporic plant. The appearance of synapsis Just 
Previous to the formation of the tetraspores, followed by two succes- 
