JOUENAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



MARCH, 1920. 



TRANSACTIOXS OF THE SOCIETY. 



I. — Studies on the Binucleate Phase in the Plant-cell. * 



By Agnes Arber, D.Sc, F.L.S., Keddey rietcher-Warr Student 

 of the University of London. 



(Bead February 18, 1920.) 

 One Plate and Two Text-figb. 



Introduction. 



In a recent paper, by Mr. Rudolf Beer and the present writer, in 

 the Proceedings of the Royal Society,t attention has been drawn 

 to the occurrence of binucleate or multinucleate cells in the young 

 vegetative tissues of 177 species, representing 60 families, and 

 including members of the Pteridophytes, Gymnosperms, Dicotyle- 

 dons and Monocotyledons. The binucleate condition, which in 

 these cases occurred as a normal feature, was invariably found to 

 arise through mitosis, and not by direct division. It was shown 

 that, though the cell-plate makes its appearance as usual, it fails 

 to give rise to any cell-membrane, while the whole complex of 

 spindle fibres with the associated cytoplasm becomes transformed 

 into a hollow sphere which encloses the daughter nuclei. For this 

 spherical shell we have suggested the term " phragmosphere." 

 The phragmosphere is seen in section in a number of the examples 

 drawn on the plate accompanying the present paper (see, for 

 instance, figs. 7, 26 and 39 A). In the memoir cited we enume- 



^ * The writer desires to acknowledge her indebtedness to the Senate of the 

 University of London for a grant from the Dixon Fund towards the expenses of 

 tihs and other researches. 



t Beer, R. and Arber, A. (1919) and (1916). 



B 



