POLLEN MOTHER-CELLS OF DICOTYLEDONS. 



443 



succeed one another in the one or other direction, which is of 

 considerable advantage to the observer. 



Pollen-formation in Dicotyledons. In order to study the 

 processes as they take place in the pollen mother-cells of the 

 Dicotyledons, we preferably select for examination one of the 

 Eanunculacese or Papaveraceae. In what follows we will refer 

 to the stinking Hellebore, Helleborus fcetidus ; in essentials 

 other Dicotyledons offer similar conditions. In a flower-bud 

 which, with stalk, measures from ^ to 4 of an inch in height, we 

 find usually, progressing from within outwards, all the stages of 

 division represented in the successive anthers. Here, also, we 

 crush the anthers in acetic methyl-green, and obtain the same 

 figures as in Liliacece, but smaller. After the first dividing stage 

 of the mother-nucleus, a cell-plate is produced in the connecting 

 threads, but again dissolved, while the nuclei prepare for a second 

 division. The figure of the 



second division exactly re- ~B A. 



sembles the first. The pairs 

 of nuclei are joined by con- 

 necting threads. These four 

 nuclei are arranged in the 

 globular mother-cell at the 

 four corners of a tetrahedron 

 (Fig. 155, A). Because con- 

 necting threads arise free in 

 the cytoplasm in all direc- 

 tions between the four nuclei, 



it follows, therefore, that to the two systems of connecting 

 threads previously present four more are added. In these six 

 systems cell-plates arise (B). These plates are clearly visible ; 

 the connecting threads, however, are to be seen only in the most 

 favourable cases. The six cell-plates have the form of quadrants 

 of a circle ; they join one another in the interior of the mother- 

 cell. Upon the thick wall of the mother-ceU are produced six 

 internal, somewhat. projecting, ridges, and to these the cell-plates 

 join with their outer edges. Cellulose walls are quickly formed 

 in the cell-plates, and thus the mother-cell is divided into four 

 tetrahedrally arranged daughter-cells (A). These four cells soon 

 obtain their own walls, and become free, while the wall of the 

 mother-cell is dissolved. 



Another Dicotyledonous flower which may be used for this. 



FIG. 155. HeUeborus fcetidus. 

 mother-cells, at A in quadripartition ; 

 after complete quadripartitioii ( x 



Pollen 

 at B, 

 540). 



[Three only visible ; the fourth is not in focus.] 



