2i6 The Ohio Naturalist. [Vol. VIII, No. 2, 



Summary. 



1. The archesporial cell of Asimina triloba remains un- 

 differentiated during the winter, no differentiation being apparent 

 until about April 14. 



2. Tetrad megaspores are of rather frequent occurrence. 



3. The parietal layer of the ovule develops greatly. 



4. The great elongation of the embryo sac is striking. 



5. The length of time that the polar nuclei remain in con- 

 tact is quite unusual (three weeks and over). 



6. The evanescent condition of the antipodals is rather 

 unexpected in this farm. 



7. The oospore remains undivided relatively long (between 

 three and four weeks). 



8. Endosperm forms in a peculiar manner. The first wall 

 is transverse and divides the sac into two equal parts. The for- 

 mation of a linear series of endosperm now follows, continuing 

 until about a dozen cells are formed when a vertical division 

 begins at the base of the sac. 



9. The embryo is minute and imperfectly developed, even 

 in the seed. 



10. Comparatively few large microsporocytes are formed. 



11. There is a peculiar development of sterile tapetum-like 

 tissue in the microsporocytes. 



12. The pollen gi'ains are ready to be shed by May 5. 



13. The study shows that Asimina triloba differs in its 

 development from the Ranunculaceae and Papaveraceae and, 



14. Resembles the Ceratophyllaceae more or less closely in 

 its development. 



DESCRIPTION OF PLATES. 



All drawings were made with the use of the camera lucida at table dis- 

 tance. A Bausch and Loinb microscope was used with the combination 

 lenses indicated with each description. 



Fig. 1.— Sept 30, 1905. Cross section of ovulary showing undiffer- 

 entiated ovules. B. & L. 1 in.-^ in. 



Fig. 2. — Jan. 6, 1906. Section of ovule showing undifferentiated con- 

 dition still present at this date. B. & L. 1 in.-^- in. 



Fig. 3. — April 1-i, 190G. Tip of ovule showing the differentiated 

 archesporial cell. B. & L. i in.-^ in. 



Fig. 4. — April 21, 1906. Shows archesporial cell divided into parietal 

 cell and megasporocyte. The parietal cell is divided into two by a vertical 

 wall. B. & L. ^ in.-^ in. 



Fig. 5. — April 21, 1906. Tip of ovule showing incipient integuments 

 and further division of parietal layer. B. & L. 1 in.-jV in. oil iminersion. 



Fig. 6. — April 28, 1906. Shows four inegaspores arranged in a row; 

 the three upper ones are dissolving. B. & L. ^ in.-^ in. 



Fig. 7. — April 28, 1906. Shows extensive parietal tsisue and four 

 megasporocytes, the two outer divided by a vertical wall. B. & L. J in.- 

 i in. 



Fig. 8. — April 28, 1906. Same as Fig. 7. — Four megaspores, the two 

 outer ones divided by a vertical wall. B. & L. ^ in.-^ in. 



