THE HIGHER CRYPTOGAMIA. 409 



of the cells of the latter, coupled with the deposition of new 

 cellular layers on the inner side of those first formed, the 

 embryo-sac is soon (within the space of a week) filled for 

 the second time with closed cellular tissue. 



The development of the endosperm of Taxus is far 

 more simple. The rudiments of the embryo-sacs are here 

 represented (as has been already mentioned) by several 

 larger cells situated in the middle of the lower portion of 

 the nucleus of the ovule, surrounded by cellular tissue 

 arranged in scale-like layers (PI. LXIII, fig. 2). Soon after 

 the shedding of the pollen the tissue surrounding those 

 cells becomes loosened (PL LXIII, fig. 4). The growing 

 embryo-sacs begin to increase considerably in size ; this 

 increase in many instances continues to go on in one only 

 of the embryo- sacs ; the growth of the others is arrested, 

 they become shrivelled, and at last, like the loosened cells 

 of the surrounding tissue, they are dissolved and displaced 

 by the one embryo-sac (PL LXIII, figs. 5 — 8). Often 

 however two of these larger cells grow and form embryo- 

 sacs. The nucleus of the cell destined to form the embryo- 

 sac is soon absorbed, and the cell then usually assumes the 

 shape of a flask (PL LXIII, fig. 5). Two new nuclei soon 

 appear contemporaneously in its upper part, embedded in 

 the mucilaginous layer which clothes the inner wall. More 

 and more nuclei soon make their appearance in the lower 

 part also of the young embryo-sac in a similar position 

 (PL LXIII, figs. 6, 7). At first they often have no nucleoli, 

 but at a more advanced period of growth the latter are 

 never wanting. A cell is formed around each of the nuclei 

 which are deposited upon the inner wall of the embryo-sac 

 (PL LXIII, fig. 8). The walls of the young cells soon close 

 upon one another, and thus the embryo-sac is filled with 

 closed cellular tissue, except at its young upper end, where 

 nuclei are found which for a long time continue to float 

 freely (PL LXIII, fig. 9), until at last, at this end also, the 

 formation of parenchyma proceeds. In those Abietmeee 

 whose seeds ripen the first year, the embryo-sac is filled, a 

 few days after the shedding of the pollen, with a closed 

 tissue of large cells (PL LXII, fig. 11), by whose con- 

 tinual multiplication in all three directions the endosperm 



