June, 1923] 
YOUNG 
GERM CELLS IN THE POTATO 
335 
Plate XXVI 
Fig. 1. Embryo sac, one-nucleate stage. 
Fig. 2. First nuclear division in embryo sac. 
Fig. 3. Embryo sac, two-nucleate stage. 
Fig. 4. Embryo sac, four-nucleate stage. 
Fig. 5. Embryo sac, four-nucleate stage just before the final division of the nuclei. 
The sac has grown to nearly its full size and has become slightly curved. 
Fig. 6. Ovule containing fully developed embryo sac. At this stage the ovule 
consists almost entirely of the greatly thickened integument, the cells of which, surrounding 
the embryo sac, are enlarged and form a jacket of nutritive tissue. The integument does 
not close completely over the embryo sac. A narrow micropyle leads from the pointed end 
of the sac to the outside. The synergids are seen as small, pear-shaped cells in the micro- 
pylar end of the embryo sac, each having a large distal vacuole. The deeply staining egg 
lies close beside the synergids and has a large basal vacuole. The two polar nuclei lie side 
by side in the central portion of the embryo sac. These fuse later to form the primary 
endosperm nucleus. The three deeply staining antipodal cells occupy the base of the 
embryo sac. 
Fig. 7. Disintegration of embryo sac. 
Lookout Mountain. X 680. 
Plate XXVII 
The integument is shown in 
Fig. 1. Disintegration of megaspore and nucellus. 
outline. 
Fig. 2. Disintegration of embryo sac at a later stage of development than that shown 
in PI. XXVI, fig. 7. 
Fig. 3. Early stage in degeneration of archesporial cells of anther. 
Fig. 4. Degenerative changes in the pollen mother cells. 
Fig. 5. Degenerative changes following heterotypic division. 
Fig. 6. Degenerative changes following tetrad formation. 
Fig. 7. Degeneration of young pollen grains. 
Fig. 8. Degeneration of nearly mature pollen characteristic of congenital pollen 
sterility. 
Fig. 9. Normal pollen grains previous to differentiation of generative and tube 
nuclei. 
Figs, i, 2, 8, and 9, Beauty of Hebron. Fig. 3, 
Russet. Figs. 6 and 7, Mammoth Prolific. X 680. 
Early Ohio. Figs. 4 and 5, Dibble’s 
24 
