1918] NOTHNAGEL—FERTILIZATION I51 
stages (fig. 3), and still later, in the spirem stage, a large nucleolus 
is frequently observed (fig. 9); but at the beginning of segmentation 
all traces of these nucleoli have vanished. 
With the beginning of segmentation, the chromatin threads 
appear to contract, presenting the appearance of “‘the second con- 
traction”’ of heterotypic mitosis (figs. 11, 12). Following this, the 
nuclear membrane surrounding the two groups disappears, leaving 
the massed segments lying free in the cytoplasm. Even now the 
two sets of chromosomes are separate (fig. 12), and to all appear- 
ances a spindle is formed about one group of chromosomes and the 
other set is pulled into the bipolar spindle, for, as late as in fig. 13, 
the chromosomes contributed by the sperm are distinct from those 
contributed by the egg. In each of the two groups (fig. 13) there 
are approximately six chromosomes, or the haploid number. The 
writer was unable to determine the arrangement of these two sets 
upon the equatorial plate, owing to lack of material for later stages. 
From the number of chromosomes seen at telophase and later 
divisions, each splits longitudinally at metaphase, so that twelve, 
the diploid number, pass to each pole. 
Discussion 
A very full, detailed account of fertilization in Pinus by FER- 
GUSON and in Abies by Hutcutnson has been published; but a 
similar account is not to be found for angiosperms. 
FERGUSON (5) reports that in Pinus the chromatin of the egg 
is arranged in an interrupted reticulum, the network consisting of 
granules of various sizes in a colorless linin. When the contents of 
the pollen tube have been discharged into the egg, one of the male 
nuclei takes up a position on the concave side of the egg, this depres- 
sion having been formed at the approach of the male nucleus. 
Gradually from each nucleus a spirem is formed from the respective 
chromatin material, at which period fibers arise in the region of 
the spirems and the nuclear membrane gradually fades away. At 
segmentation these two spirems give rise to two groups of chromo- 
somes, but as they collect on the spindle this distinction is lost. 
Each chromosome splits longitudinally and each daughter nucleus 
receives the diploid number. When these daughter nuclei are 
Preparing for second division, the chromatin collects into two 
