224 



REPRODUCTION 



Fig. 128. — Stages in the division of a grandmother cell of microspores or pollen grains 

 of a lily, somewhat d agrammatic. i, resting stage of grandmother cell; 2, nuclear thread 

 becoming arranged into parallel threads; 3, synaptic stage; 4, parallel threads uniting; 5, 

 double threads so united as to appear as one; 6, threads again separating; 7, thread trans- 

 versely segmented into double chromosomes; 8, diakinesis, that is, chromosomes dispersed 

 about the nuclear membrane; 9, multipolar spindle stage; 10, bipolar spindle with double 

 chromosomes aligned at the equator; 11, reduction division, the double chromosomes 

 separating and at the same time showing longitudinal division, with the longitudinal halves 

 widely apart at their equatorial ends; 12, formation of daughter nuclei, which are really the 

 nuclei of the mother cells of the spores; 13, division of mother-cell nuclei, the longitudinally 

 split chromosomes seen in 1 1 again appearing; 14, split chromosomes of 13 aligned at 

 the equator ready for the longitudinal halves of each to be drawn apart to opposite 

 poles; IS, separation of the longitudinal halves; 16, formation of the granddaughter 

 nuclei, or nuclei of the spores. (After Strasburger.) 



