CELL-DIVISION. JI 



The question now remains whether in all micro- and macro-spore 

 mother-cells of the higher plants a double longitudinal splitting of the 

 chromatin takes place during the first mitosis and how prevalent such 

 a phenomenon is in both plants and animals. 



In those plants in which the daughter nucleus passes into the struc- 

 ture of the complete resting stage, it is certainly difficult to understand 

 the significance of the double longitudinal splitting of the chromosomes 

 in the first division. 



CELL-DIVISION. 

 THE TYPE OF THE HIGHER PLANTS. 



Modern research has established the very important fact that new 

 cells are formed from uninucleate or multinucleate mother-cells accord- 

 ing to different methods, depending largely upon the manner in which 

 the new plasma membranes differentiating the cells are formed. 



(i.) Among the higher plants, and some Thallophyta as well, in 

 which cell-division is generally intimately associated with nuclear 

 division, the new plasma membrane or membranes are laid down 

 through the instrumentality of kinoplasmic connecting fibers, extending 

 between the nuclei concerned. 



(2.) In the ascus of certain Ascomycetes, where the new cells 

 (spores) are carved out of a common nucleated mass of cytoplasm or 

 mother-cell, the plasma membrane is also formed by kinoplasmic 

 fibers, but these are polar radiations and not connecting fibers. The 

 entire plasma membrane of such cells is new, that of the mother-cell 

 taking no part in the process. This is typical and real free cell- 

 formation. 



(3.) Another form of cell-division is found among the Myxomycetes 

 and certain Phycomycetes, in which the new plasma membranes arise 

 by a process of progressive cleavage, beginning at the surface, with or 

 without any connection with, or aid of, vacuoles. Kinoplasmic con- 

 necting fibers or radiations are in no way connected with this process. 

 This type we may know as cell-cleavage. It resembles the cleavage of 

 animal cells more closely than do the other processes of cell-formation 

 in plants. 



(4.) There is yet another method of cell-formation typified by 

 Dictyota and Stypocaulon among the brown algae, in which the new 

 plasma membrane seems to be a direct transformation of the meshes 

 or threadwork of the cytoplasm. It is not a cleavage like the last 

 mentioned, nor are any connecting fibers present to take part in the 



