22 2 Ferguson . — Development of the Pollen- tube and the 
Fig. ii. The same at a later date, showing a slight increase in the size of genera- 
tive cell, x 540. Pinus Strobus, Oct. 7. 
Fig. 12. The pollen-tube which is shown in Fig. 2, more highly magnified. 
X 540. Pinus Strobus , Jan. 4. 
f ig- I 3* A pollen-grain and the upper portion of a pollen-tube, showing the 
stalk- and the generative cell just before their passage into the pollen-tube, x 540. 
Pinus austriaca , May 3. 
Figs. 14 and 15. Later stages than the above, showing the passage of the 
generative and the stalk-cell into the pollen-tube; in Fig. 15 the two cells are 
breaking loose from each other, x 540. Pinus austriaca , May 10 and 17. 
Fig. 16. The male gametophyte at the time of the entrance into the tube of the 
generative and the stalk-cell; n. t., a bit of the dead nucellar tissue, x 540. 
Pinus Strobus , June 9. 
Fig. 17. A pollen-grain after the generative and the stalk-cell have passed into 
the pollen-tube ; taken from the top of the nucellus of Fig. 4. x 540. Pinus 
Strobus , June 9. 
Fig. 18. A few of the cells from that portion of the nucellar cap marked n. c. 2 
in Fig. 4. The cells are filled with starch-grains, x 540. Pinus Strpbus , 
June 9. 
PLATE XIII. 
Figs. 19-21. Portions of pollen-tubes showing successive stages in the passage 
of the stalk-cell over the generative cell, as also the presence of large quantities of 
starch in the pollen-tube, x 540. Pinus resinosa, June 2 ; P. Strobus, May 24 ; 
P. rigida , June 8. , 
Fig. 22. The generative cell, bearing on its surface both the vegetative and 
stalk-nuclei. In this instance the stalk-cell has passed beyond the vegetative 
nucleus, x 540. Pinus resinosa , June 3. 
Figs. 23-25. The generative cell in the early stages of its division, showing 
granular condensation and radial arrangement of cytoplasm. x 850. Pinus 
rigida , June 8 and 10. 
Fig. 26. A later stage of the same, x 850. Pinus austriaca , June 10. 
Fig. 27. The generative cell just before the disappearance of the lower portion 
of the nuclear membrane, x 850. Pinus Strobus , June 9. 
Figs. 28 and 28 b . Two sections through the same generative cell. In Fig. 28 
the section was cut through the edge of the nucleus and shows the spindle-fibres 
passing over the outside of it. Fig. 28 b represents a section nearer the middle of 
the nucleus : the nuclear wall has given way at the centre and is fading out along 
the entire lower portion of the nucleus ; some spindle-fibres are entering the nuclear 
cavity, while others stretch along the surface of the disintegrating membrane. 
Neither section was cut parallel to the major axis of the growing spindle, x 850 
Pinus austriaca , June 10. 
Fig. 29. A stage in spindle-formation directly following that shown in Fig. 27. 
X 850. Pinus Strobus , June 10. 
Figs. 30-35. Later stages in the development of the spindle, showing the gradual 
drawing together of the outer extremities of the threads to form the upper pole of 
the spindle, as also the origin of the chromosomes, x 850. Fig. 33, Pinus rigida , 
June 13 ; the other figures, Pinus austriaca , June 7-10. 
Fig. 36. A cross-section through the generative cell during an early stage in its 
