Sticdies on the Binucleate Phase in the Plant-cell. 3 



of complete rest (PI. I, fig. 1). The same aggregation of cytoplasm 

 has been noticed in the case of Dipsacus laciniatus. In some 

 preparations of the prothallus of Cephalotaxus Fortunei, at the stage 

 when the cells are becoming multinucleate, which Mr. Boodle has 

 kindly shown to me, the relation of the cell protoplasm to the 

 dividing nuclei is exactly similar to that just described for 

 Eremurus, the cytoplasmic bridles being particularly well 

 developed. 



The formation of binucleate cells proceeds exactly on the lines 

 described in general terms in the paper already cited.* While the 

 daughter nuclei are passing into rest, the chromosomes go through 

 a stage in which they each show a large vacuole (PL I, figs. 8 and 

 ^). That such paired nuclei retain the power of further division 

 is shown by the fact that a phragmosphere, with its two included 

 nuclei, may be accompanied, in the same cell, by a resting nucleus 

 (PI. I, fig. 7). This indicates that the cell previously enclosed a 

 pair of nuclei, one of which has divided again, while the other has 

 remained in the resting condition. This is of some interest, since 

 it means that two sister nuclei, necessarily of identical age and 

 living apparently under identical conditions within- a single 

 Tegetative cell, are yet capable of showing marked individuality in 

 their behaviour. 



In the previous generalized account of the development of the 

 phragmosphere (I.e. p. 10), it is stated that a cell-plate is formed 

 but disappears later. It may, however, be objected that when two 

 daughter nuclei are observed with a cell plate between them (as in 

 PI. I, fig 4) there is no proof that the development of a phragmo- 

 sphere will follow, since the appearance in question might equally 

 well be interpreted as an early stage in actual cell-wall formation. 

 The conclusion that such stages are both hona fide members of the 

 phragmosphere series is based on the fact that in the inflorescence 

 described there is no evidenc3 of any recent wall formation in 

 planes parallel to the long axis of the organ ; a cell plate such as 

 that figured could form a wall in such a plane only. The cells both 

 of the pith and of the ground tissue between the bundles have 

 a rounded outline, as seen in transverse section, and intercellular 

 spaces occur between them. This is true of all the inflorescences 

 studied, even the very young one to which attention will be called 

 shortly. The only exception is found in certain small cells in the 

 pith which contain raphides and mucilage, and which divide fairly 

 frequently. But these cells are quite distinct in their characters, 

 and the occurrence of wall formation in them does not affect our 

 argument ; our figures and descriptions refer to the normal pith and 

 ground tissue, and not to these specialized cells. In order to test 

 the contention that the increase in diameter of the axis depends 



» Beer, E. and Arber, A. (1919) p. 10. 



B 2 



