1900] LIFE HISTORY OF SILPHIUM 129 
PLATE Ill 
All figures magnified 130 diameters. 
Fic. 1. First appearance of individual florets: d, disk floret; 7, ray 
floret; 47,, 672, bracts on receptable ; 2z, involucral bract. 
Fic. 2. A later stage: parts lettered as in fig. 7 
Fics. 3-11. Successive stages in development of disk floret: each part 
lettered on its first appearance: cor, corolla tube; s¢, stamens; 4, carpels; 
m, nectaries ; Pa, pappus. 
Fics. 12-21. Stages in development of ray floret: cov, corolla tube; sé, 
stamens; %, carpels; ov, ovule; the base of the subtending bract indicates 
the anterior side of the floret. 
Fic. 21, a. Lateral section of floret whose median section is shown in fg. 
27. st, rudimentary stamens. 
PLATE IV 
Figs. 22-27, magnified 130 diameters; jigs. 28, 29, magnified 1375 diame- 
ters 
FIG. 22. S. integrifolium. Ray floret when archesporial cell first becomes | 
recognizable in ovule. 
1G. 23. Ray floret: nucellus (7) just appearing. 
Fic. 24. S. integrifolium. Older ray floret, ovule half turned: sé, half 
developed stamen; #, nectary; course of vascular bundles shown by dotted 
li 
Fic. 25. S. integrifolium. Ovule at time of first division in archesporial 
cell: au, nucellus; 77, integument. 
1G. 26. S. integrifolium. Ovary of older floret, showing nectary, rudi- 
mentary pappus, ovule, and course of vascular bundles. 
S. integrifolium. Ovary and ovule at time of maturity of 
embryo sac. 
Fig. 28. S. integrifolium. Details of ovule outlined in fig. 22, showing 
archesporial cell. (Safranin-gentian-violet. 
FIG. 29. S. integrifolium. Nucellus of older ovule; nucleus of arche- 
sporial cell with one nucleolus and eight chromosomes. (Cyanin-erythrosin.) 
PLATE V 
All figures magnified 1375 diameters. 
FiG. 30. S. perfoliatum. Spindle fully formed in archesporial cell; chro- 
mosomes in equatorial plate. (Iron-alum-haematoxylin.) 
IG. 31. S._integrifolium. Nucellus with row of four potential megas- 
pores. (Saf.-gen.-violet.) 
Figs. 32, 33. S. integrifolium. Growth of fertile megaspore and its 
encroachment upon the sterile cells. (Saf.-gen.-violet.) 
