SUMMARY 925 
ved (fig. 22). The wall of the nucleus then disappears and soon after the 
gemini are seen in the cytoplasm. The multipolar spindle is then formed 
(fig. 7), and is followed by a bipolar one. In the bipolar spindle the biva- 
lent chromosomes, are scattered through the whole of the spindle-figure 
B 8). In the later stages of the bipolar spindle they are so arranged 
that they form the aequatorial plate. This stage is favourable to the 
counting of the number of chromosomes. The anaphase and telophase 
of the first division take place in the usual way (fig. 9, 25 en 12). The 
anaphase is also a suitable stage for the counting of the chromosomes. 
The next stage is the interkinesis. The chromatic substance clings to 
the wall of the nucleus (fig. 10). After interkinesis another contraction 
was observed similar to the one after diakinesis. This is the fifth con- 
traction (fig. 26). On the bipolar spindle the chromatic substance is 
scattered all over the spindle, as described in the case of the hetero- 
type division (fig. 27). In the metaphase of the homoötype division the 
number of chromosomes could not be determined (fig. 28). The ana- 
phase, telophase and the formation of the pollen-tetrads proceed nor- 
mally. In the tetrads as well as in young pollen-grains a radiation of 
the cytoplasm could be seen around the nucleus. 
The cultivated species of wheat may be divided into 3 groups, accor- 
ding to their chromosome numbers. This division corresponds roughly 
to the one founded on different degrees of sterility, on serological be- 
haviour and on susceptibility to certain diseases. 
The wild T. dicoccoides Kcke. var. Aaronsohnit Percival forms an 
exception, as it enters into the monococcum-group (IT. monococcum 
L.) according to the number of chromosomes; into the dicoccum-group 
(T. dicoccum, T. turgidum, T. durum, T. polonicum) according to 
physiological relationships. 
