362 Digby . — The Cytology of Primula kewensis 
together like beads on a string (Fig. 3). At first they take the stain lightly, 
but as they increase in volume and in definity they become more and 
more chromatic. Gradually the limits of the beaded individual chromo- 
somes become discernible, and fine threads are seen connecting the beads of 
one chromosome to those of another (Fig. 4). Then the beaded appearance 
becomes less and less marked, until finally it blends into the homogeneous 
chromosome with a smooth outline (Figs. 5 and 6). The chromosomes go 
on to the spindle, and the neat compact equatorial plates are most charac- 
teristic. It is only when on the equatorial plate that the longitudinal 
fission in the substance of each chromosome becomes discernible. 
Thus the different manner in which the formation of the mature 
somatic chromosome is accomplished in the Primulas as compared with 
Qnaphose Telophase Rest Prophase mefap'hase 
Text-fig. i. Somatic division. 
such forms as Allium ( 21 ), Galtonia ( 9 ), &c., is simply due to the fact 
that in the Primulas the longitudinal halves of the portions of segment- 
ing chromosomes during telophase tend to remain together, whereas in 
Allium , &c., the longitudinal halves of the portions of segmenting chromo- 
somes during telophase tend to separate (Text-fig. 1). In this latter case the 
separation of the two halves results in two parallel threads, each of which 
is a portion of the longitudinal half of a somatic chromosome. During 
the ensuing prophase these longitudinal halves come together again to form 
the whole somatic chromosome, but often this union is incomplete, leaving 
a space (longitudinal fission) between the halves which will take effect and 
separate the two daughter chromosomes when they are arranged on the 
equatorial plate. On the other hand, in the Primulas, the homogeneous, 
unsplit chromosome of the telophase breaks across transversely into por- 
tions, which therefore represent pieces of whole somatic chromosomes. 
During the ensuing prophase these whole pieces come together end to end, 
