1905] SHATTUCK—ULMUS AMERICANA 221 
EXPLANATION OF PLATES VII-IX. 
All figures were made with an Abbé camera lucida and reduced one-half in 
reproduction. Figures with a magnification greater than 600 diameters were 
made with a Zeiss apochromatic objective 2™™, ap. 1.30, and Zeiss compensating 
oculars 4, 8, and 12. All others with Spencer 5™™ and 16™™ objectives and 
oculars 4 and 8. 
The abbreviations employed in describing fhe figures are as follows: 7, 
flower; pt, pollen tube; po, polar nuclei; e, egg; en, endosperm nucleus; ed, 
endothecium; s, stigma; sy, synergids; smc, spore mother cells; /, fusion nucleus; 
at, antipodals; m, male cell; mm, megaspore; 0, ovule; 07, outer integument; 
ii, inner integument; tm, tube nuclei; ¢, tapetum; gv, generative nucleus; cr, 
crown cells; m, nucellus; sh, stigmatic hair. 
‘ Fic. 1. Young flower showing stigma protruding and ready for fertilization. 
12. 
Fic. 2. Flower cluster showing filaments and flower stalks in the center as 
first to elongate. x5. 
1G. 3. Winter stages of microsporangium showing mother cells. 600. 
1G. 4. Later stage showing the organization of tapetum from peripheral 
mother cells; other mother cells in synapsis. > 600. 
Fic. 5: Section of microsporangium showing enlargement of endothecium, 
the breaking down of the tapetum, and the two inner layers of cells of the sporan- 
sium walls; also tetrads dissociating. 600. 
Fic. 6. Microspore mother cell in first mitosis. 1260. 
Fic. 7. Second mitosis of microspore mother cell. 1260. * 
45 8. Four-nucleate mother cell preparing to form tetrads. 1060. 
-9. Tetrads within the mother cell. x 1000. 
: Fic. ro. Microspore showing tube and generative nuclei and openings in the 
exine, X 1260. 
Fic. 11. Portion of the exine showing holes through which pollen tubes 
emerge. X 1200, 
Fic. 12. Division of generative nucleus to form male cells. 1260 
Fig, 13 Male cells ne a ; ae 
ee attached by their adjoined ends; tube nucleus disin- 
tegrating. 1260 : : 
Fic. 14. Male cells free and encircling disintegrating tube nucleus. X 1260. 
air. x 
16.18. Microspore showing five tubes emerging; all equal in size. X 1260. 
Fic. 19. Mi 
. 19. Microspore showing five emerging tubes; one in contact with the 
stigmatic hair. 1569 . oe : : 
Fig, 20. Tw 
Fy 
: erating microspore showing cyst formed at end of stigmatic 
6 2g pollen tubes entering the same micropyle. 45°. 
«ar, Branching pollen tubes. X 200. 
