158 I'SE BOTANICAL MAGAZINE. CVoi. xxxv. No. 417. 



excluded from the daughter nuclei ; (3) some univalent chromosomes 

 get into the spindle, not at the equator, but very near to the one 

 pole ; therefore notwithstanding their being split into two halves, the 

 halves pass to one and the same pole, instead of being carried to the 

 opposite poles ; (4) in some material the split univalent chromosomes, 

 left outside the daughter nuclei, serve a bridge connecting the 

 daughter nuclei, (PI. Ill, Fig. 20) the result is a dumbell shaped 

 nucleus very much like the abnormal nuclei which were got by 

 Sakamura in his interesting experimental study (1920). Some of 

 these irregular large nuclei contract afterward and become rounded, 

 so they do not show any difference compared with the normal 

 nuclei, except the abnormally large size and the much larger number 

 of chromosomes they contain. 



After the first division of the pollen mother cell, the achromatic 

 fibres of the spindle disappear gradually and many granules appear 

 at the equatorial region of the mother cell, but no partition 

 membrane is formed. 



At the interkinesis, chromosomes become irregular in shape and 

 size, and are connected each other with fine protrusions. No 

 nucleolus appears in the latter stage (PI. Ill, Fig. 14, 15). When 

 the second division soon starts and chromosomes are established, the 

 large chromosomes split longitudinally, but the small ones do not. 

 The former may be interpreted as derived from the bivalent chromo- 

 somes, while the latter from the univalent ones. The divided 

 chromosomes arrange themselves to form the equatorial plate first,. 

 and after they reached the anaphase, the undivided chromosomes 

 come into the spiudle which is bipolar from the beginning (PI. Ill, 

 Fig. 16, 17). The axes of the two spindles are net in a definite 

 relation, sometimes parallel, sometimes perpendicular, and sometimes 

 inclined to each other. The second equatorial plate is always 

 somewhat irregular. The distribution of the imdivided chromosomes 

 is not even, so that very often in the telophase many chromosomes 

 are left in the cytoplasm (PI. Ill, Fig. 18). They maj- be single or 

 in groups of two or more, and being surrounded by a membrane, 

 partial or miniature nuclei (PI. Ill, Fig. 25j are formed. So the 

 pollen mother cell frequentlj' contains one or more small nuclei in 

 addition to the normal or larger nuclei. When pollen grains are formed 

 in the mother cell, some of the miniature nuclei may get into a 

 pollen grain, together with the normal nucleus (Text-fig. 1, c), but 

 sometimes the miniature nucleus with accompan3'ing cytoplasm may 



