﻿2 lO 



BOTANICAL GAZETTE 



[march 



^^4 --U 



a 



3 



a 



2 



a 



\ 



and a^ are parallel or 



It soon divides by a periclinal wall, forming a primary tapetal cell and 

 a sporogenous cell. The primary tapetal cell subsequently divides by 

 two anticlinal walls at right angles to each other, forming four (rarely 

 two) tapetal cells which closely resemble the reproductive cells in size, 

 contents, and staining qualities {figs, /, 2), Other investigators (4, 



11) have noted similar processes of 

 division in monocotyledonous plants. 

 The sporogenous cell, by two divisions, 

 forms an axial row of four potential 

 macrospores ; frequently these divi 

 sions occur by walls all of which are 

 perpendicular to the long axis of the 

 ovule {fig. /), but more often the walls 

 between a^ 



oblique to the axis of the ovule 

 (/^- ■^)- So far as I know, no case 

 has been reported where four poten- 

 tial macrospores have the arrange- 

 ment shown in fig. 2, 



An axial row of four macrospores 



has been reported in a number of 



plants, some of the best-known cases 



being the Gramineae (3), many of the 



Rosaceae (i, 14), Elodea, Triglochin, 



Carex, Polygonum (3), Avena (9), Canna (11), Eichhornia, Pontederia 



(8), and probably in Potaviogeton Nutans (12) and 



Lilaea siibulata (7). Three macrospores occur in 



Orchis (i, 14), Allionia, Gomphrena, Geum (3), 



Naias and Zannichellia (6), two in Convallaria 



Fig. I. 



foliosus 



and Arisaema 



triphyllum (4), except that in the last named they ^ 

 Stand side by side instead of forming an axial row. 



1 



When the wall between 



fis 



nearly parallel to the plane of the section the axial 

 row appears to have only three macrospores, but 

 careful focusing shows that a^ and a^ lie one above 

 the other. The cell at the basal end of the row is 

 usually triangular. 



Three of the cells of the row disintegrate. The survivor becomes 

 the embryo-sac. There are indications that any one of the four mac- 



1/ 

 / 



P'iG. 2. 



