No. 466.] STUDIES ON PLANT CELL. VIII. 723 



brane. Or the area may be a cell plate whose halves on division 

 finally merge with outer plasma membranes of the cells. The 

 spindle fibers which cut out the spore areas in the-ascus form 

 the basis of a plasma membrane. Thus the fate of all kinoplas- 

 mic fibrillae seems to be a final return to the undifferentiated, 

 finely granular condition so characteristic of plasma membranes 

 which according to this theory is the condition from which they 

 arose. 



Thus I believe the liverworts present rather striking evidence 

 of a relationship between the centrosphere, polar cap, and the 

 free fibrillar condition of spindle formation and establish an 

 evolutionary tendency from the first two types of kinoplasmic 

 differentiation towards the latter. The free fibrillar type of 

 spindle formation is found in a very simple form in this group, 

 sometimes with temporary centers, as in the four-rayed figure 

 (quadripolar spindle) of prophase, whose poles have accumula- 

 tions of kinoplasm in the position of centrospheres. The polar 

 caps are likely to prove a much simplified type of centrosphere 

 whose kinoplasm is no longer gathered to form conspicuous 

 spherical centers. With respect to the problem of the homol- 

 ogies and nature of the blepharoplast, the liverworts furnish as 

 yet no material assistance and this structure stands at present 

 as one of the most interesting puzzles of plant cytology. As 

 stated in the beginning, the variety of centrosomes and centro- 

 spheres with and without radiations in various types of the thal- 

 lophytes seems to me too confusing to promise an understanding 

 of their relationships at present. 



Gregoire and Berghs (: 04) have interpreted the structure of 

 the mitotic figure in the germinating spore of Pellia in a very 

 different manner from the accounts of Farmer, Chamberlain, 

 and myself. They consider the asters to arise through a re- 

 arrangement of the cytoplasmic network around the nucleus. 

 They affirm that there are no true centrospheres nor any ac- 

 cumulations of granular kinoplasm to constitute the centers of 

 origin for the spindle fibers or the radiations around the poles of 

 the spindle. The centers of the asters ("vesicules polaires ") 

 are said to have a vesicular structure and neither they nor the 

 nucleus contributes to the building up of the spindle which is 



