BoT.— Vol. II.] BYXBEE—LAVATERA. 69 



The planes of division of the daughter nuclei do not seem 

 to be at all constant. Sometimes they divide in the same 

 plane, sometimes in planes at right angles to each other, and 

 there are all possible transitions between these two. Figure 

 22 shows a cell in which the planes are at right angles to 

 each other and fig. 23 one in which they are nearly parallel. 



The four daughter nuclei resulting from the second divi- 

 sion become surrounded by granular zones just as did the 

 nuclei resulting from the first division. These zones are 

 usually very broad and dense. Connecting them are the 

 mantle fibers across which the cell-plates are formed later 

 on. (fig. 24). 



The granular zone persists even in the pollen-grain, at 

 least while it is young (fig. 25). It usually occupies at least 

 one-third of the cell space outside of the nucleus. The 

 cytoplasm outside of the zone also contains a great deal of 

 granular matter. 



The most important fact in the method of spindle forma- 

 tion above described is that the spindle is formed from free 

 fibers and not from a network. That part of the cytoplas- 

 mic reticulum which aids in the formation of the spindle is 

 converted into free fibers at an early stage, long before the 

 nuclear wall breaks down (figs. 5, 6, etc.). The linin net- 

 work of the nucleus breaks up at an even earlier time. 

 The fibers derived from these two sources become inter- 

 woven but never form a true network. 



The granular zone, too, is more than usually prominent 

 in Lavatera. Its significance will be discussed later. 



The higher plants hitherto most exhaustively studied, as 

 Equisetiim (Osterhout, 1897), Larix (Belajeff, 1894), 

 Cobcea (Lawson, 1898), and Passijloi'a (Williams, 1899), 

 all show a certain general resemblance to each other and to 

 Lavatera in the method of forming the spindle in the repro- 

 ductive cells. No two of them, however, agree fully in 

 the details. In all of them the first changes in the cyto- 

 plasm are either a radial elongation of the meshes of the 

 reticulum or a parallel drawing out of the first two or three 

 rows adjacent to the nucleus. 



