Division of the Generative Nucleus in Pines. 221 
EXPLANATION OF FIGURES IN PLATES 
XII, XIII, AND XIV. 
Illustrating Miss Ferguson’s paper on the Pollen-tube of Pines. 
All figures were drawn by the aid of the Abbe camera lucida, the image being 
thrown down only 143 mm. A Zeiss microscope was used and (with the exception 
of Figs. 1-5 and 44) the 2 mm. homogeneous immersion objective. This objective 
was combined with the compensating ocular No. 8 for Figs. 23-43, 46, and 46 b ; 
for all other figures the compensating ocular No. 4 was used. The figures are 
reproduced from the drawings without reduction. Throughout the plates the 
lettering is to be interpreted as follows : third prothallial or antheridial cell ( a . c.), 
vegetative nucleus ( v . n.), stalk-cell ( st . c.), stalk-nucleus ( st . n.), generative 
cell (g. c.), generative nucleus ( g . n.), sperm-cell ( s . c.), sperm-nucleus ( s . n .), 
prothallium (Pr.), spongy tissue (s. t.), archegonium ( arch .), and starch grains 
(*•*■•)• 
PLATE XII. 
Fig. 1. A vertical section through an ovule some days after pollination ; A. r., 
axial row; p. g, pollen-grain, x 70. Pinus Strobus , June 17. 
Fig. 2. A vertical section^of an ovule showing the winter condition, x 70. 
Pinus Strobus, Jan. 4. 
Fig. 3. A vertical section of an ovule soon after the second period of growth 
has begun, x 7 °* Pinus Strobus , May 26. 
Fig. 4. A vertical section through the upper part of an ovule at the time of the 
division of the generative nucleus; n. c. 1, that portion of the nucellar cap which 
was developed during the first period of activity; n. c. 2, that part of the nucellar 
cap which constitutes the second year’s growth ; 0, disintegrating spongy tissue, 
x 70. Pinus Strobus , June 9. 
Fig. 5. A vertical seetion through the upper part of an ovule shortly before 
fertilization; e. n., egg nucleus; 0, last vestige of spongy tissue, x 70. Pinus 
Strobus , June 15. 
Fig. 5 b. Pollen-grain from the nucellus of Fig. 5. The antheridial cell is still 
undivided, x 540. 
Fig. 6. Mature pollen-grain ; p. 1 , first prothallial cell ; p . 2 , second prothallial 
cell, x 540. Pinus Strobus , June 8. 
Fig. 7. A vertical section through the extreme upper portion of an ovule soon 
after pollination, showing the uppermost part of the nucellar cap, and a pollen- 
grain in the first stages of germination ; P. c., pollen-chamber, x 540. Pinus 
Strobus , June 13. 
Fig. 8. A pollen-grain soon after germination ; p ?, second prothallial cell, 
x 540. Pinus Strobus , June 24. 
Fig. 9. A pollen-grain after the vegetative nucleus has passed into the pollen- 
tube. x 540. Pinus Strobus, July 15. 
Fig. 10. A pollen-grain after the antheridial cell has divided, x 540. Pinus 
Strobus , Aug. 4. 
