238 



INTRODUCTION TO CYTOLOGY 



assumed the form of a continuous spireme which is double. This double- 

 ness is believed to represent a true longitudinal split, and although it 

 usually disappears from view during the later prophases it is thought to 



Fig. 90. — The heterotypic prophases in Lilium, according to Mottier (1907.) 



A, synizesis knot loosening up; threads splitting; note chromomeres. B, hollow spireme. 

 C, second contraction. D, diakinesis. X 900. 







■ 



2) 



m 



, ■ 



- ' 







-s, 



Fig. 91. — Maturation mitoses in microsporocyte of Vicia faba. 



A, anaphase of heterotypic mitosis; split for second mitosis evident in separating 

 daughter chromosomes. B, one daughter nucleus in early telophase of heterotypic mitosis. 

 C, later telophase. D, metaphase of homceotypic mitosis. E, anaphase of same, showing 

 portions of both spindles. F, three of the four microspore nuclei. X 1335. (After 

 Fraser, 1914.) 



persist and reappear at a much later stage. After extending loosely 

 throughout the nucleus ("open spireme"), the double spireme, now con- 

 siderably thickened and twisted (strepsinema) , contracts again and is 



