April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 355 



the plorome-element ; in other words the greater portion of 

 the monaster occupies the apical half of the archesporium, 

 i.e., the half lying next the dermatogen, and the position 

 of the chroniatin-segments gives us an indication as to the 

 level at which the cell-plate will be laid down later on. 

 The monaster figured shows two sets of filaments or fibrils, a 

 set of thick, deeply stained and centrally placed ones to 

 which the chroniatin-segments are attached, and a peripheral 

 set of delicate feebly stained ones, to which no chromatin- 

 segments are attached. 



In a later stage of division (fig. 6), in which the new cell- 

 wall is being laid down in the form of granules we note 

 an inequality in the size of the two daughter-cells x and y, 

 the cell y lying next the plerome-elements being the 

 larger, the nucleus of the cell y is elongated radially, 

 i.e., the long axis of the nucleus is parallel to the long axis 

 of the mother-cell, while the nucleus of the cell x is elongated 

 tangentially, i.e., the elongation is at right angles to the 

 long axis of the mother-cell. The meaning of this difference 

 in the shape of the two nuclei becomes evident on studying the 

 future history of the two cells derived from the archesporium 

 (figs. 7 and 8). In fig. 7 the nucleus of the cell x has 

 become still more broadened out tangentially ; in fig. 8 it is 

 represented as a diaster ; and in fig. 9 division has been 

 completed. Similarly we find in fig. 7 the nucleus of the 

 cell y of fig. 6 in the diaster stage, and its division completed 

 in fig. 8. Thus the cell x (fig. 6) has divided anticlinally 

 (fig. 9), while the cell y (fig. 6) has divided periclinally 

 (fig. 8), and we must look upon the slightly oval shape of 

 the two nuclei x and y (fig. 6) at this early stage of nuclear 

 reconstruction as an indication of what will take place later 

 on : — each nucleus is already elongated at right angles to 

 the plane of division, and therefore its long axis corresponds 

 to the direction of the nuclear barrel. 



Four cells are thus derived from the physiological arche- 

 sporium (figs. 2, 3, 4, ^.aS'.), as the latter divides firstly by a 

 periclinal wall (fig. 6) into a larger basal cell y, and a 

 smaller apical cell x, and as the cell y redivides periclinally 

 into two cells (y and JS.S., figs. 7, 8) ; the cell x redividing 

 anticlinally into two cells (figs. 7, 9'"*). Only once I found 

 the apical cell x to divide undoubtedly periclinally (fig. 9*^), 



