CURRENT LITERATURE 



NOTES FOR STUDENTS 



Phragmospheres and binucleate cells. — Beer and Arber t maintain that 

 there is a binucleate phase during the development of the parenchymatous 

 tissues of the higher plants, which is preceded, and usually succeeded, by a 

 uninucleate phase. They conclude that the binucleate condition is invariably 

 brought about by mitosis, and state: 



The division occurs normally in the earlier stages, up to the period at which 

 the two daughter nuclei are at the poles of the spindle, while the cell-plate is just 

 being initiated. But at this point the mechanism seems to break down and the cell- 

 plate is resorbed, while the phragmoplast, with its associated cytoplasm, goes through 

 a singular metamorphosis. It becomes vacuolate in the center and develops into 

 a hollow sphere which gradually grows until it incloses both the daughter nuclei, and 

 then, by its further extension, ultimately merges into the cytoplasm lining the cell 

 wall. For this hollow shell we have proposed the term "phragmosphere." In some 

 cases it is exceedingly well defined and stains deeply, giving the sections in which it 

 occurs a curious appearance of exhibiting cells within cells. 



The writer 2 recently has described certain cytological phenomena which 

 appear to be significant in this connection. In longitudinally dividing cells 

 of the cambium of the higher plants the central spindle expands laterally by 

 the addition of peripheral fibers, and gradually assumes the form of a disk. 

 The connecting fibers and later the accessory fibers thicken to produce a cell 

 plate and then disappear, leaving a circular rim of kinoplasm. In tangential 

 longitudinal sections of the cambium, this ring-shaped aggregation of kino- 

 plasmic fibrillae, phragmoplast, forms a halo about the daughter nuclei and 

 gives the impression of a "cell within a cell." It increases in circumference, 

 by the addition of new peripheral fibers, until it intersects the radial facets of 



1 Beer, R., and Arber, Agnes, On the occurrence of binucleate and multi- 

 nucleate cells in growing tissues. Ann. Botany 29:597-598. 1915. 



, On the occurrence of multinucleate cells in vegetative tissues. Proc. 



Roy. Soc. B. 91:1-17. 1919. 



Arber, Agnes, Studies on the binucleate phase in the plant cell. Jour. Roy. 

 Micr. Soc. March 1920. 1-21. 



2 Bailey, I. W., Phenomena of cell division in the cambium of arborescen 

 gymnosperms and their cytological significance. Proc. Nat. Acad. Sci. 5:283-285 



1919. 



, The formation of the cell plate in the cambium of the higher plants. 



Proc. Xat. Acad. Sci. 6:197-200. 1920. 



, The significance of the cambium in the study of certain physiological 



problems. Jour. Gen. Physiol. 2:519-533. 1920. 



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