MITOSIS IN POLLEN MOTHER-CELLS. 19 
the points of the crescents to form ring-like chromosomes (Fig. 9, D, 
at the right). In the majority of cases, however, they adhere at only 
one end, and under such circumstances each chromosome consists of 
two thick and slightly curved pieces placed end to end, and as they 
are oriented tangentially upon the spindle, reach nearly from pole to 
pole (Fig. 9, D). 
The chromosomes in Podophyllum present the same variety of forms 
found in Lilium and Tradescantia. Here the segments may be in 
close contact, side by side, or form loops, rings, X’s, and Y’s. Per- 
haps the majority of chromosomes in Podophyllum present the form 
last mentioned for Zradescantia. 
In Lzdéum the chromosomes, when in the nuclear plate, are usually 
arranged with much regularity about the periphery of the spindle. 
The majority are fastened to the fibers at the ends, and stand radially 
to the axis of the spindle (Fig. 7, H). When observed from the pole 
in this stage, they are seen to radiate like the spokes of a wheel from 
the central spindle fibers. But all the chromosomes are not so regu- 
larly oriented upon the spindle, and their manner of attachment to the 
fibers is also variable. As will be seen in Fig. 8, F-K, they may be 
fastened to the spindle at some distance from one end or near the mid- 
dle. Those that are quite regularly ring-shaped are attached near the 
middle of each segment. In all these cases, the chromosomes are 
placed tangentially upon the spindle. The X-, Y-, and loop-shaped 
chromosomes are usually fastened to the spindle as indicated in Fig. 
8, F, J, K. Karyokinetic figures are not rare in which two or more 
of the different forms of chromosomes, with their different orientations 
and different methods of attachment to the fibers, are found in the 
same spindle.’ 
The stage of the mature spindle persists some time and evidently 
1 Other interpretations of the chromosomes appearing in the first mitosis have been given by different 
observers and by the same investigator at different times, owing to the trend of theoretical considerations. 
One of these, which was announced as early as 1884 by Heuser for Tradescantia virginica (Beobach- 
tung iiber Zellkerntheilung. Bot. Centralbit.,17: 1884) and which has very recently received support by 
Strasburger and others (Ueber Reduktionstheilung. Sitzbr. der Konig. Preuss. Akad. der Wiss., 18: 
1-28, 1904) is that the two segments of each chromosome appearing in the equatorial plate of the first 
mitosis are not the result of the longitudinal splitting of the spirem occurring in the early prophase, but 
are formed by the folding together or approximation of two chromosomes, each consisting of the two 
daughter segments resulting from the longitudinal splitting. ach chromosome is therefore a bivalent 
chromosome, and the first or heterotypic mitosis is a qualitative or reducing division, whereas the second 
mitosis is equational, the segments separating along the line of the longitudinal split. Strasburger bases 
his conclusion mainly upon data obtained from studies of the pollen mother-cells of Galtonia candicans. 
The figures which he gives in support of this view in the paper cited seem tu me to be far from convinc- 
ing. Moreover, Jules Berghs, in a recent study of the prophase of the heterotypic mitosis in Al/ius 
Jistulosum and Lilium lancifolium (speciosum) (La Cellule, 21: 173-188, 1904), shows clearly, ina careful 
series of stages, that the two segments of each chromosome are the result of the longitudinal fission and 
not that of a folding together or approximation of two chromosomes, Unfortunately the papers cited 
reach me too late for further consideration, as these pages are already in press. 
