298 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



tyledons and of the larch, where in the latter case the division is 

 by a cell-plate, makes the above interpretation possible whether 

 it be assumed that the membrane grows by intussusception or 

 apposition. There is no reason for presuming that the radiating 

 fibers may not contribute to the growth of the plasma membrane 

 as well as do the spindle fibers. 



Considering the tetranucleate cell with the constriction furrows 

 (fig. 30) as a whole, it will be noted that inasmuch as there are 

 six spindles, no two of which are parallel, there will be six furrows. 

 Three of these furrows come together above each point of con- 

 tiguity of three spindles. In other words, there are four points 

 on the surface of the mother-cell at each of which three furrows 

 meet. These points are the centers of the four faces of the tetra- 

 hedron. Each of these points of intersection is equidistant 

 from the three nuclei, the mutual spindles of which are bisected 

 by these furrows. Since the median line of each furrow is the 

 arc of a circle which is smaller than a great circle of the tetra- 

 nucleate cell, the points of deepest depression of these furrows are 

 at their points of intersection, consequently there are four pro- 

 jections of the plasma membrane into the protoplast. Since the 

 mother-cell-wall conforms to the plasma membrane exactly, the 

 condition might be described as four equidistant invaginations 

 of the mother-wall, each of which is connected with the others 

 by a ridge upon the inner surface of the wall. These projections 

 proceed gradually toward the center of the cell, keeping equidistant 

 from the three nearest nuclei, and growing toward the fourth. 

 It is thus apparent that these four projections finally meet in the 

 center of the tetranucleate cell, before the furrows have com- 

 pleted the division in the equator of each spindle (fig. 32). 



The first indication of the growth of these projections toward 

 the center of the mother-cell is in the straightening of the spindle 

 fibers noted above (fig. 30). This straightening results in the 

 fibers pulling away, from the center of the mother-cell, leaving a 

 space which is triangular in section, but is really pyramidal, in 

 the center of the cell. The eccentric position of the projection 

 of the mother- wall shown in figure 31 is not typical, and is 

 doubtless due to the failure to cut all three spindles in the median 

 plane, the one on the lower right side being cut near the periphery 

 of the spindle. Figure 32 gives the typical condition. The 



