CYTOLOGICAL STUDIES ON CEREALS AND THEIR HYBRIDS. 



183 



into many pieces, thus the increase of chromosomes in number is caused, and al the same 

 time their size and form are not uniform. By observing the bivalent chromosomes going 

 to the pole and also the very long chromosomes in the spindle, it is made clear thai the 



spindle formation begins at the time of spirem as shown in Fig. 81 of PI. XII; and the 



very often the segmented chromosomes, the curved spindles and manv paired chromosomes 

 (PL XIII. Fig. 91, 92). In some cases, the paired chromosomes arc separated again by 

 means of .secondary spindle fibres (PI. XII. Fig. 89). Besides the chromosomes, many chro- 

 matic granules are visible in the cytoplasm as observed by many cytologists in the plant 

 hybrids (PI. XII. Fig. 89; PI. XIII. Fig.. 98, 99, 100). 



Judging from the deficiency of cytoplasm in the pollen mother-cell of the hybrid, 

 it may be proved that when the quantity of chromatin reaches a definite ratio to that of 



Polypodium, etc. — the augmentation of chromosomes and their scattered arrangement must 

 have been produced by the abnormally premature formation of the spindle. The primary 



leads to the abnormal mitosis. The chromosomes which form the daughter nuclei, trans- 

 form into spirem as in rye (PI. XIII. Fig. 99). Besides the two daughter or four grand- 

 daughter nuclei, there is formed often a dwarf nucleus in the place where one or more 

 chromosomes are left behind (PI. XIII. Fig. 94). 



In the second division only a large irregular chromatic mass is visible in the equa- 

 torial plate (PI. XIII. Fig. 98) and a few smaller chromatic masses are found in other 

 parts of the spindle. 



There are besides some abnormal figures, such as three spindles in a pollen mother- 

 cell (PI. XII [. Fig. 93), or the case in which one daughter nucleus is in the resting state 

 while the other is in mitosis (PI. XII. Fig. 87). 



In spite of the many irregular processes, the perfect tetrad can be observed in some 

 loculi, chromosomes changing into spirems or fine granules, which are produced by the 

 breaking up of the spirem. Six pollen grains are sometimes formed through three separate 

 spindles in the common membrane of the mother-cell (PI. XIII. Fig. 97). The pollens of 

 the hybrid differ in size among themselves. The results of my present study confirm the 

 statement,— that the large pollens have many chromosomes, while the smaller ones have a 

 few,— which has been made by other authors in other cases. 



