1906] YAMANOUCHI—POLYSIPHONIA VIOLACEA 433 
the carpospore and constitutes a part of the sporophyte generation 
that begins with the fertilized carpogonium . 
This long sporophytic phase terminates with the formation of 
tetraspores, when a reduction of chromosomes takes place, 20 chromo- 
somes entering each tetraspore. These tetraspores with the reduced 
number of chromosomes evidently have returned, with respect to 
nuclear conditions, to the potentialities of the original gametophyte 
or sexual generation. Again, it may never be possible to grow spore- 
lings from the tetraspore to maturity under experimental conditions, 
but it is evident that plants derived from the tetraspores must have 
nuclei with 20 chromosomes. The sexual plants of Polysiphonia are 
the only forms in which 20 chromosomes are found, therefore it may 
safely be concluded that the sexual plants arise from tetraspores. The 
tetraspore then constitutes an indispensable part of the life history 
of Polysiphonia, and cannot be regarded simply as an accessory type 
of reproductive structure, such as is illustrated by many forms of 
asexual spores in the thallophytes or by the gemmae of bryophytes. 
To summarize the life history of Polysiphonia, the gametophyte 
§eneration begins with the tetraspores and ends with the sexual cells 
or gametes, whose fusion initiates the sporophyte generation; this 
covers a long period, including the formation of carpospores, germina- 
tion of Carpospores, development of the tetrasporic plants, and at 
last ends with the formation of tetraspores. In other words, the 
sexual plants and the tetrasporic plants present the two distifct phases 
of an antithetic alternation of generations, with the cystocarp a part 
of the sporophytic phase, The life history of Polysiphonia may be 
tabulated as follows: 
Gamet hut; * Pp g 
E g 
| 
(Germination) Doubling of cheats (Germination) Reduction of chromosomes 
T ~ ey a T 
etraspore—s nucleus (20 EE Ty, ic plant-Tetras| 
(20). : wt eae —_———— oe pita (20, 
nucleus (20) 
Taking up the theories concerning the life history of the red algae, 
OLTMaNNs (55) concluded eight years ago, from an investigation of 
{our genera (Dudresnaya, Glocosiphonia, Callithamnion, and 
Dasy a), that the structure derived from the fertilized carpogonium 
