44 
ON THE EMBRYOLOGY OF CARPINUS BETULUS. 
Fig. 3. Basal part of an embryo-sac, showing the polar nuclei, p.n., almost fused, and the generative 
nucleus, g.n., travelling towards them through the cytoplasm. 
4. Upper part of an embryo-sac showing the egg-cell, e.c., and the two synergidz, S. A pollen- 
tube, p.t., runs up one side of the sac, and abuts on the two polar nuclei, p.a. Within the 
tube can be seen the two generative nuclei, g.n., and the vegetative nucleus, v.n. 
5. Diagram constructed from a series of sections, showing the course of a pollen-tube, p.t., first in 
the wall, and then in the lumen of the embryo-sac, e.s.; the tube is arrested before reaching 
the egg-cell. 
5a. A portion of the same enlarged, showing a late stage of triple fusion, and the strand of 
protoplasm, S., along which the generatiye nucleus, g.n., has probably travelled. 
6. Two embryo-sacs with egg-cells, e.c., e./c.', and definitive nuclei, d.n., d.'n. The course of the 
pollen-tube, is shown, and the liberation of the generative nucleus, g.n., by means of a spur, s. 
6a. The definitive nucleus, d.n., of the previous figure, with the generative nucleus, g.n., about to 
fuse with it. 
7. A pollen-tube, p.t., entering the cecum of an embryo-sac at the level of the polar nuclei, p.n. 
8. The upper part of an embryo-sac, showing the egg-cell, e.c., and the definitive nucleus, d.n. 
The pollen-tube contains two generative nuclei and the vegetative nucleus close together 
in a group, g.n. A plug, a, has been formed, probably preparatory to the liberation of one 
of the gametes. 
9. Shows the entry of a pollen-tube, p.t., into an embryo-sac, close to the spot where the polar 
nuclei, p.n., lie. These include the tube between their elongated lower ends. One synergid, S., 
is seen by the side of the egg-cell, e.c., which is not yet surrounded by a wall. 
10. Fertilization of an egg-cell, e.c., by a coiled generative nucleus, g.n. p.t., tip of pollen-tube; 
v.n., vegetative nucleus. 
11. Shows a pollen-tube, p.t., running between the ceca of several embryo-sacs. The tip of the 
tube is collapsed, and the loss of both generative cells to the neighbouring definitive 
nuclei, d.n., is suggested. ch., the chalaza. 
