458 THE AMERICAN NATURALIST. | (VoL. XXXIX. 
involving the development of a vegetative structure before the 
period of sporogenesis. From the studies of Wolfe (:04) we 
know that the sporophyte portion of Nemalion (the cystocarp) 
contains nuclei with double the number of chromosomes (about 
16) present in the gametophyte (about 8) and that the period of 
chromosome reduction is apparently just previous to the devel- 
opment of the carpospores (sporogenesis). Williams (: 04a and 
b) has recently determined that the asexual plant of Dictyota is 
' a sporophyte generation with double the number of chromosomes 
(32) found in the sexual plant (16). The reduction occurs here 
during a rather long period of preparation on the part of the 
nucleus in the tetraspore mother-cell and the reduced number 
appears in the two mitoses that form the tetraspores. These 
events closely parallel those in the spore mother-cell of higher 
plants and will be discussed further under “ Sporogenesis.” 
William’s (:04b) account of gametogenesis in Dictyota is the 
most complete that we have for any thallophyte. The oögonia 
and antheridia are cut off from a stalk cell by a mitosis which 
presents 16 chromosomes, the number characteristic of the 
gametophyte. The contents of the oögonium forms a single 
egg and consequently presents no mitotic phenomena. The 
antheridium develops over 1500 sperms thus exhibiting a large 
number of successive divisions. These all show 16 chromosomes 
and the mitoses are typical, not differing in any essential from 
the division in the stalk cell. The entire absence of mitoses in 
the oógonium and the great number in the antheridium are 
striking facts which show that no especial significance can be 
attached to nuclear divisions within sexual organs of this type. 
There is no place for reduction phenomena within these sexual 
organs and none precede their development. 
These studies of Williams and Wolfe justify us in expecting . 
that other thallophytes will support their discoveries that the 
product of the sexual act will have a fusion nucleus with double 
the number of chromosomes present in the sexual plant (game- 
tophyte) and that reduction phenomena may be expected to fol- 
low the sexual act and not precede it as in animals. In such 
thallophytes as have no sporophyte generation we may suppose, 
as Strasburger (94a) suggested, that the number of chromo- 
