18] LIFE HISTORY OF THE PONTEDERIACEA 327 
 erceptible is the undulated outline of the placenta as seen in 
ngitudinal section (fg. 7). In older flowers the placentz 
lave become distinctly papillate. The dome-shaped promi- 
sences shown in fig. g are the young ovules. They are not 
wanged in regular rows, but are scattered so that every cross 
- ection runs through two, three, or four to each placenta. 
At this time, or a little later, the archesporial cell is first appa- 
rat. Its nucleus is larger and less deeply stained than those of 
the surrounding tissue, while its cytoplasm is more dense and 
: ‘tains more deeply, especially with erythrosin (fig. 5)- As the 
ovule enlarges the archesporial cell divides unequally by a peri- 
chinal wall into an outer primary tapetal cell, and a larger pri- 
Mary Sporogenous cell (fig. 6). The primary tapetal cell may 
main undivided, but usually it divides into two by an anticlinal 
wall. The plane of division is either parallel to the axis of the 
lower, asin fig. 7, or at right angles to this axis, as in fig.g. The 
 Mapetal cells at once begin to lose their characteristic staining, 
: ad before their final disappearance are distinguishable from the 
ther cells of the hypodermal layer only by their position. If, 
| towever, the primary tapetal cell does not divide, it retains its 
“aining reaction more or less persistently to the last. The axial 
 'W of which the archesporium is the terminus also divides 
|r tows (fig. 7). 7 
i la further course of development of the primary ope 
; bite cell may be along two entirely different lines, which lead 
oe ver to the same result, viz., the formation of a row of four 
- ™Raspore mother cells, of which only the lowest one is fertile. 
She aa series may be compared with those figured in Stras- 
: BE “ Angiospermen und Gymnospermen for 77 yitomia aurea and 
: Spor m ramosum respectively. In the one case the primary 
: _ cell gives rise at once by successive divisions to a 
- i four cells, of which the lowest is always much the largest 
-" 9). In the other case, most common in | 
“the py: gation of the ovule is accompanied by an elongation © 
a Primary Sporogenous cell without division of the latter (jigs. 
Mand 
é T ‘ : 
2). The nucleus also enlarges and invariably remains at 
