1908] GATES—REDUCTION IN OENOTHERA 23 
PLATE 1 
IGS. I, 2.—Young meristematic cells of anther primordium showing one 
large nucleolus and several smaller ones, and chromatic masses adherent to the 
nuclear membrane. 
Fic. 3.—Longitudinal section of anther, showing size relations of nucleoli in 
Sporogenous, tapetal, and wall cells. 
F 
IG. 4.—One sporogenous cell from stage o SB. 3, previous to synapsis; 
oS ie somewhat vacuolate. 
Fics. 5, 7-9.—Nuclei at same stage, showing fusions of nucleoli. 
1G. 6.—Two nucleoli of equal size; an unusual condition. 
Fic. 10.—Several small nucleoli, and no indication of fusion. 
Fic. 11.—Nucleoli of young pollen grain nucleus. 
Fic. 12.—Beginning of synaptic contraction; the reticulum has contracted 
from the nuclear membrane on all sides, leaving several loops attached to the 
membrane; on the side on which the reticulum retains the curved outline of the 
nuclear membrane the latter has been drawn inward attached to the threads; on 
the rest of the circumference, between the loops, the nuclear membrane remains 
in situ; the cytoplasm is perfectly fixed. 
Fic. 13.—Another contraction stage, showing loops attached to the nuclear 
membrane, which is intact. 
Fic. 14.—A slightly later stage of contraction, in which the rearrangement 
of threads is taking place. 
Fic. 15.—Synapsis; dark-staining bodies are still held in the meshes of the 
spirem; a small nucleolus, usually about the size of a chromosome, is generally 
present in addition to the large nucleolus. . 
Fic. 16.—After synapsis; the thread thicker and shorter and loosely coiled. 
Fic. 17.—Slightly later stage than fig. 16, and less deeply stained; thread 
shows the characteristic light and dark areas; indications of parallel threads in 
two places; edge of thread may be even or moniliform.—s5 # 
Fic. 18.—Later stage; thread much shortened and greatly thickened and 
entering upon second contraction phase; nucleus uncut.— 
Fic. 19.—Higher magnification of a portion of the tivead in figs. 20 and 21. 
PLATE II 
1G. 20.—Second contraction stage; a pair of chromosomes cut off from 
spirem; nucleus uncut.—1o x. 
Fic. 21—Second contraction stage; nucleus uncut. 
Fic. 22. —Unocoiling from second contraction stage; pair of chromosomes 
‘ detached; nucleus uncut. 
1G. 23.—Spirem segmented in three places, each segment showing constric- 
tions which will form the chromosomes; certain chromosomes already detached; 
spars uncut. 
G. 24.—Constriction of spirem has proceeded farther, the chromosomes being 
shangited bodies with irregular margins like the spirem, and connected by rather 
