MINNESOTA BOTANICAL STUDIES. 



Explanation of Plates. 



The drawings were made with the aid of a camera lucida and reduced 

 nearly one-half. The magnifications indicated are those to which they 

 were originally drawn before reduction. The figures on plate III, (num- 

 bers 30-40 inclusive), are photo-micrographs and are reduced the same as 

 the drawings. 



Fig. I. Longitudinal section through the inflorescence, about 19-20 months 

 before blossoming. X 16. 

 Longitudinal section through ovary showing single ovule. X 82. 

 Longitudinal section through ovary showing several ovules. X 82. 

 Longitudinal section of ovule showing archesporial cell and "tape- 

 tal" layer to the outside. Several periclinal divisions in the 

 micropylar end of the nucellus have taken place. Archesporial 

 or spore-mother cell in a stage of synapsis. Fall condition. X 630. 

 Fig. 5. Spore-mother cell shortly after growth has been resumed in the 

 spring. Nucleus showing spireme. X 840. 

 First division of spore-mother cell. X 840. 

 Second division of spore-mother cell. Outer spindle is seen in 



transverse position. X 840. 

 Four megaspores, two of which are lying in the longitudinal, the 



other two in the transverse axis of the nucellus. X 840. 

 Four megaspores, the two outer lying over each other giving the 

 appearance of only three being present. The fourth nucleus 

 is faintly visible. X 840. 

 Four megaspores in a nearly straight row. X 840. 

 Germination of megaspores. Nuclei of the two inner megaspores 

 dividing. X 720. 

 Fig. 12. Eight-celled stage of the embryo-sac showing four nuclei at either 

 end and the remnants of megaspore nuclei at the micropylar end. 

 X 840. 

 Fig. 13. Embryo-sac showing antipodal cell, definitive nucleus, egg appa- 

 ratus and remains of megaspore nuclei. X 620. 

 Fig. 14. Two-celled embryo, endosperm nuclei and three antipodal cells. 



X 620. 

 Fig. 15. Young embryo consisting of three cells. Two endosperm nuclei 



dividing. X 630. 

 Fig. 16. Free cell formation in early stages of endosperm development. 



Antipodal cells becoming prominent. X 420. 

 Fig. 17. Polar nuclei approaching and meeting near the middle of the sac. 



X 720. 

 Fig. 18. Three much enlarged antipodal cells. X 720. 

 Fig. 19. Suspensor in contact with endosperm. X 720. 

 Fig. 20. Development of endosperm tissue, appearance of walls after a 



period of free cell formation. X 720. 

 Fig. 21. Young embryo and surrounding endosperm. Antipodal tissue in- 

 vading the latter. X 325. 

 Fig. 22. Section through ripe ovule showing integuments. X 82. 



