Jan., 1907.] 
Synapsis and Synizesis. 
43 
stage in the life cycle of every sexual organism containing defi¬ 
nite chromosomes. The fusion of the chromatin in synapsis can¬ 
not have any important effect on the hereditary characters of the 
chromosome. At the most the effect is probably the same as that 
which may be experienced in the fusion of the chromatin during 
each resting period of the nuclei in the entire history of the “2x” 
stage. It is the association of the chromosomes in the oospore 
and the subsequent vegetative history that appears to be of im¬ 
portance whether the chromosomes are closely mingled and 
fused or not. And it must be apparent that hereditary tenden¬ 
cies are active both in the resting stage of the nucleus and in the 
process of karvokinesis. 
The early longitudinal splitting of the spirem in the first re¬ 
duction division may be looked upon as a continuation of the 
usual process of vegetative karvokinesis, the quantitative separa¬ 
tion of the daughter parts being interfered with by the interca¬ 
lation of the synaptic stage. Since the separation or segregation 
of the univalent chromosomes follows immediately, a second 
division spindle is organized through the influence of the double 
chromosomes and thus normal nuclei are again produced by the 
distribution of the daughter halves. The mere presence of these 
chromosome pairs in the daughter nuclei resulting from reduction 
may be the cause of the rapid formation of the second spindle, 
and the explanation of the quite general presence of cell tetrads 
following the reduction division in both plants and animals. 
Yet it is hardly permissible to say that the first and second divi¬ 
sions are not true karyokineses. Nevertheless, the second div- 
sion is a karvokinesis which had its beginning in the previous 
stage which was interrupted by the intercalation of the synapsis 
and reduction processes. The first spindle formed was taken 
advantage of by the bivalent chromosomes and the segregation 
following being of paternal and maternal double chromosomes 
the second spindle became necessary for the separation of the 
daughter pieces. In the first division the number of chromatin 
granules is not reduced although only half the original chromatin 
granules are represented in the daughter nuclei because of the 
transverse division of the chromosome as shown by me in the 
reduction division of Lilium philadeiphicum* In such cases 
as in the megasporocytes of Lilium, where the process of 
spore formation has been abbreviated, the vegetative division 
following the reduction is of the same nature as the second divi¬ 
sion when the usual spore tetrads are produced. This was defi¬ 
nitely shown to be the case in my paper on Erythronium albi. 
*Schaffner, John H. (Contribution to the Life-history of Lilium 
Philadeiphicum). The Division of the Macrospore nucleus. Bot. Gaz. 
23 : 430-452, 1897. 
