152 



INTRODUCTION TO CYTOLOGY 



and even in root cells occasionally (Fig. 73, 10) the late prophasic karyo- 

 lymph assumes the orientation characteristic of the spindle, and the 

 attachment regions of the chromosomes move to the equator as the 

 membrane disappears without shrinking inward. Cases are also known 

 in which the partially shrunken membrane disappears when in some inter- 



wmm. 



\' '" " • •■■■ ■ 





• m'.-' ' :^' /*,' I... 





'7 





>■ 



D 







k1 w*# 





-■, mji /v:>o'./- .\ (•■•' i/'-'ft^;^-?^'®-'^^. ■i^:.\ .(fe ::.--'■■■".-.-••. .-.1 







■^ 



^ 





^■■^^ ■ ■ 



v-;':> 







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Fig. 82. — Development of achromatic figure in microsporocyte of Larix europcea. 

 A-H, after fixation in Benda's fluid. I-L, after fixation in Flemming's fluid. L and H 

 show two successive stages in cytokinesis. {After Devise, 1922.) 



mediate position. Hence it becomes easy to reconcile the many early 

 accounts in which the spindle was variously stated to arise from the cyto- 

 plasm, from the nucleus, or from both. What was being observed in all 

 these cases was a progressive transformation of the late prophasic karyo- 

 lymph, or nuclear "spindle substance," into a polarized spindle, with or 

 without a shrinkage of the nuclear membrane before its disappearance. 

 The reactions involved in this transformation are unknown, but it has 



