certain Penaeaceae. 
'ill 
EXPLANATION OF FIGURES IN PLATES XXV AND XXVI. 
Illustrating Miss Stephens’s paper on the embryo-sac and embryo of certain Penaeaceae. 
Abbreviations used : end. endosperm ; em. embryo ; e.s. embryo-sac ; e.s.zu. embryo-sac wall ; 
int. integument ; m.m.c. megaspore mother-cell ; nuc. nucellus ; o. oospore ; peri, periblem ; pi. 
plerome; b.g. peripheral group; p.n. polar nucleus; p.t. pollen-tube. 
PLATE XXV. 
Fig. i. Longitudinal section through young ovule, showing megaspore mother-cell, a periclinal 
division in the cell-layer above it, and developing integuments, x 390. Sarcocolla squamosa. 
Fig. 2. Longitudinal section through upper part of nucellus and embryo-sac (at stage of Fig. 13), 
showing a second undivided megaspore mother-cell (?) above the embryo-sac. x 390. Sarcocolla 
squamosa. 
Fig. 3. Longitudinal section through ovule just prior to division of the megaspore mother-cell, 
in the nucleus of which synapsis is beginning, x 390. Sarcocolla minor. 
Fig. 4. Nucleus of megaspore mother-cell, showing synapsis, x 1300. Penaea mucronata. 
Fig. 5. The same, showing chromosomes, x 1300. Penaea mucronata. 
Fig. 6. Longitudinal section of metaphase of first (heterotype) division of megaspore mother- 
cell. x 1300. Sarcocolla minor. 
Fig. 7. Optical section of embryo-sac, made up of two successive transverse sections, showing 
metaphase of second (homotype) division, x 1300. Penaea mucronata. 
Fig. 8. Optical section, made up of two successive transverse sections, showing telophase of the 
same, x 1300. Sarcocolla minor . 
Fig. 9. Four-nucleate embryo-sac, slightly older than that of Fig. 8, showing tetrahedral 
arrangement of nuclei. The nucleus marked a really lies at the same distance from the one that 
overlies it in the figure as it does from the two others, x 630. Sarcocolla minor. 
Fig. 10. The same, showing different arrangement of nuclei, x 600. Sarcocolla formosa. 
Fig. 11. Later stage, showing nuclei separating. The nuclei marked a and 13 occur at the 
beginning and end respectively of the series of longitudinal sections composing this embryo-sac; the 
other two lie about its middle, x 630. Sarcocolla minor. 
Fig. 12. Later stage ; nuclei in prophase of division, x 420. Sarcocolla minor. 
Fig. 13. Eight-nucleate embryo-sac. x 420. Sarcocolla formosa. 
Fig. 14, a and b. Same stage but with five groups of nuclei; the fifth group is shown in 14 b. 
(Fixed in acetic alcohol and much contracted, so that the embryo-sac wall can be seen ; imbedded 
in it are the nuclei of disorganized nucellar cells), x 420. Sarcocolla squamosa. 
Fig. 15. Later stage; nuclei in prophase of division, x 333. Sarcocolla squamosa. 
Fig. 16. Sixteen-nucleate embryo-sac. x 420. Sarcocolla squamosa. 
Fig. 17. Later stage ; cell-walls are being formed in the peripheral groups ; one nucleus in each 
remains free ( p.n .). x 630. Penaea mucronata. 
Fig. 18. Later stage ; the free nuclei are moving to the centre of the sac. x 420. Penaea 
mucronata. 
Fig. 19, a, b. Later stage ; the free nuclei are meeting in the centre of the sac. The fourth 
peripheral group lies in a plane perpendicular to the other three, and is seen in 19 b in transverse 
section, x 420. Sarcocolla squamosa. 
Fig. 20, a-d. Successive stages of nuclear fusion ; in b, a fusion of five nuclei. All x 420. 
a, b, c, Sarcocolla squamosa ; d, Penaea mucronata. 
Fig. 21, a-e. Diagrammatic outline of five embryo-sacs, showing varying positions of the 
peripheral groups. The upper half of d is shown in Fig. 22, and of e in Fig. 23. 
Fig. 22. Upper half of embryo-sac of Fig. 21 d. with three nuclei fusing to form the primary 
endosperm nucleus. The two peripheral groups shown contain only one and two cells respectively, 
the remaining two groups are normal, x 630. Sarcocolla squamosa. 
D d 2 
