EXPLANATION OF THE FIGURES. 487 



FIG. 



8. A similar pollen-cell, already divided into two cells, treated with caustic 



potash and freed from the exine by rolling under the covering glass, 

 X 300. 



9. Pollen-cell of Pinus Larix, taken from the nucleus of an ovule in the middle 



of May. The exine has been stripped off by the swelling of the intine, 

 X 400. 



10. Longitudinal section of an ovule of a cone of Pinus Austriaca (just opened) 



at the beginning of June, x 150. 



11. Longitudinal section of the nucleus of an ovule of Pinus Mughus from a 



cone just in flower, x 300. 



12. Embryo-sac of the same species, somewhat later, after the dissolution of 



the central nucleus, X 500. 



13. Embryo sac of Pinus sylveslris with the neighbouring cells, which are be- 



coming detached ; beginning of June, x 500. 



14. Longitudinal section of the nucleus of the ovule of a cone of the same 



species which has lately flowered (beginning of June). The pollen-tube 

 has already penetrated rather deeply into the nucleus, x 100. 



15. Fragment of a detached embryo-sac of Pinus Austriaca, in the middle of 



June. Numerous free secondary nuclei are attached to the inner wall, 

 X 300. 



16. Longitudinal section of the embryo-sac of Pinus sylvestris, filled with cellular 



tissue ; end of June, X 300. 



17. Ovule and basal portion of the spermophore of Pinus maritima, at the be- 



ginning of January of the second year. The walls of the cells of the 

 very advanced endosperm (E) are much thickened by the addition of 

 layers of gelatine. Two pollen-grains (P) have emitted tubes for a short 

 dislance only into the nucleus, x 50. 



18. A single cell of the endosperm at the same time, treated with tincture of 



iodine. The primordial utricle of the cell is contracted, x 300. 



19. A single cell of the endosperm of the same species in the middle of March. 



The thickening layers of the cell-wall are already almost dissolved ; only 

 the primary membrane of the cell is still intact, x 300. 



20. Fragment of the membrane of the embryo-sac of Pinus Strobus cut through 



longitudinally, with some endosperm-cells loosely attached to the inner 

 side ; at the beginning of April, x 300. 



PLATE LX. 



1. Longitudinal section of the embryo-sac of Pinus sylvestris, at the begin- 



ning of April of the second year, x 30. 



1*. One of the cells of the interior, x 300. 



2. Embryo-sac detached, at the beginning of May. A layer of newly-formed 



cells has attached itself firmly to the inner side of the hardened mem- 

 brane of the embryo-sac, which has now entirely displaced the loosened 

 cells of the surrounding portion of the nucleus, x 30. 



2*. Portion of the outer side of the embryo-sac of the latter figure, x 300. 

 It will be seen that the cells attached to the inner wall of the embryo- 

 sac are not yet firmly attached to one another at the surfaces of contact 

 with the latter. 



