— 170 - 



Explanation of the plates. 



All figures are drawn with the aid of a camera lucida. and with a 

 Zeiss apochromatic 1,5 mm. objective. 1,30 ap.: Figs 1—15, 17, 21 and 

 29 with compens. oc. 12; Fig. 22 with compens. oc. 18; Figs 16, 18 

 —20, 23—27, 30-32 with compens. oc. 6; and Fig. 28 with objective 

 Stiassnie No. 7 and ocular No. 4. 



Plate I. 



Figs 1—7, Hieracium auricula, Pollen mothercells: 



Fig. 1, Resting stage before synapsis; 



Figs 2, 4, 5, Synapsis; 



Fig. 3, Tangential view of portion of nuclear reticulum before synapsis, showing 



the double prochromosomes; 

 Fig. 6, Multipolar spindle-formation: 

 Fig. 7, Anaphasis in the heterotypic division; 

 Fig. 8, H. venosum, Pollenmothercell, heterotypic spindle-figure; 

 Figs 9, 10, 77. auricula, Embryosac-mothercell ; 

 Fig. 9. Diakinesis; 

 Fig. 10, Heterotypic division; two succeeding sections; 



Figs 11 — 15, H. excellent, Pollen mothercells: 



Figs 11—14, Postsynaptic stage, with longitudinal split of the chromatin threads 



and formation of the chromosomes; 

 Fig. 15 a, b, Two succeeding sections of the heterotypic spindlefigure, with 

 bivalent and univalent chromosomes; 



Figs 16—24, H. excellent, Embryosac-formation : 



Fig. 16, Nucellus with postsynaptic stage in the nucleus of the embryosac- 

 mothercell; 



Fig. 17. Heterotypic spindle-figure; 



Fig. IS, Formation of the daughter nuclei: 



Figs 19, 20. Embryosac-formation: Taraxacum-scheme ; compare the text p. 156; 



Fig. 21, Anaphasis in the second division ; 



Fig. 22, Second division, prophasis with about 16 chromosomes; 



Fig. 23, The einbryosac-tetrad, with dwarfed nuclei; 



Fig. 24, The embryosac encroaching upon the 3 sistercells of the tetrad : 



Plate II. 



Figs 25—32, H. excellens, Embryosac-formation; 



Figs 25-27. Embryosac-tetrad and aposporic embryosac-formation {Ap): 



Fig. 28, Typical and aposporic (Ap) embryosacs, with dividing nuclei; the 

 typical embryosac in two-nucleus-stage; the aposporic in eight-nucleus- 

 stage ; 



Fig. 29. The aposporic embryosac, in two-nucleus-stage, encroaching upon the 

 full developed typical embryosac; at An an antipodal cell; 



Fig. 30, Nearly the same stage; the typical embryosac in two-nucleus-stage; 



Fig. 31, Two-nucleus-stage in the embryosac; 



Fig. 32, Two full developed embryosacs; the upper one probably aposporic. 



