186 Mottier.—Nuclear and Cell Division 
counted,and this number persists throughout the two succeeding 
mitoses. In vegetative cells the number is not far from thirty. 
In Dictyota the first nuclear division in the tetraspore 
mother-cell, as already stated, reveals the reduced number. 
Here sixteen chromosomes were counted. In vegetative cells 
the smaller size and the crowding together of the chromo¬ 
somes make counting more difficult and less accurate, but 
in several instances the number was found to be not less 
than thirty, and one may reasonably suppose that thirty-two 
is the normal number. 
The two nuclear divisions in the tetraspore mother-cells 
are strikingly similar to those in spore mother-cells of 
higher plants. The tetraspore, being borne, as it seems, by 
the gametophyte, may not be homologous with the spores 
of higher plants, and consequently to speak of the nuclear 
divisions in the former as homologous with those in the 
latter might lead to confusion. The fact that these types of 
karyokinesis occur so universally in reproductive cells of 
widely divergent groups of organisms in both the vegetable 
and animal kingdoms forces upon one the conclusion that 
they are of the utmost theoretical importance. 
If the reduction in the number of chromosomes should 
prove to be of as far reaching significance as is generally sup¬ 
posed, Dictyota offers, beyond any doubt, a most interesting 
field for speculation and further research. 
Whether in the nuclei of the seedling plants arising from 
tetraspores the reduced number of chromosomes persists, 
and whether in the egg-cell the reduced number obtains, 
are problems which further research must solve. Unfor¬ 
tunately I was unable to obtain the proper stages of karyo¬ 
kinesis to ascertain the number of chromosomes in the cells 
of the seedling plants in question, nor was the division by 
which the stalk-cell of the oogonium was cut off, observed 
so that the number in the egg might be determined. In 
this respect it is of prime importance that the sequence of 
generations, arising from the tetraspores and from the fecun¬ 
dated egg, be ascertained with accuracy, and that the number 
