POLLEN MOTHER-CELLS OF LILIACE^J. 441 



fibres which are joined on to the chromosome pairs, these latter 

 are drawn towards the spindle-poles. Of each pair of chromo- 

 somes one chromosome thus is taken to the one pole, one to the 

 other. As a result of the manner of their folding, these separating 

 sister chromosome segments show a V-like form (e, /). The 

 spindle-fibres which extend from pole to pole retain their position, 

 and serve as the needed " stays " for the contraction of the other 

 spindle-fibres. At the spindle-poles the daughter nuclei are 

 formed out of the chromosomes (</), and are soon bounded by a 

 nuclear membrane derived from the cytoplasm. The spindle- 

 fibres remaining between the poles form the connecting threads. 

 The number of these connecting threads increases in the equatorial 

 plane of the cell, and at the same time the entire system swells 

 barrelwise and becomes separated from the daughter nuclei. By 

 local swelling of the connecting threads the cell-plate now 

 arises in the equatorial plane (</), and within this is soon 

 formed a primary membrane, and immediately afterwards 

 a partition wall, which divides the cell in halves. The two 

 daughter nuclei rapidly enter into a second division, in which 

 figures arise which differ from those in the first division in not 

 unimportant details (Ji, i). As a matter of fact, in this second 

 division in the pollen mother-cells, a longitudinal cleavage of the 

 chromosomes, prior to the separation of the nuclear thread into 

 separate chromosomes, also takes place, but these longitudinally 

 cleft chromosomes do not fold together as in the first division ; they 

 are, rather, attached with their equatorial ends to the spindle- 

 fibres. In the subsequent separation of the sister chromosomes 

 in the second division, these, because not folded, show a rod-like 

 form (/). The first division with folded chromosomes, which in 

 the moment of separation appear V-shaped, is distinguished as 

 41 heterotypic division," from the ordinary processes of division, 

 which we see, as above, in the second dividing stage. From the 

 sister chromosomes of this second division arise, at the spindle- 

 poles, the' granddaughter nuclei, and between these cell-division 

 is completed in the same way as in the first division (m). The 

 division of the two sister-cells, i.e., the second division, takes place 

 either in the same plane, or in two crossing one another at right 

 angles. 



Instructive preparations are also quickly obtained by staining 

 alcohol material with fuchsin iodine-green. It is best to prepare 

 a solution of fuchsin and of iodine-green, each in 50 per cent. 



