il 
REPRODUCTION OF THE GYMNOSPERMIA. 837 
4 
nucleus and distinct cell-wall, from one of which the pollen-tube 
is developed, and which adhere to the inside of the internal 
membrane close to the point where the external membrane 
presents a slit ( fig. 1159). 
The ovules of the Gymnospermia, excluding those of the Gnet- 
acez, which require further investigation, consist of a nucellus 
or macrosporangium (fig. 1160, a), enclosed by a single coat, 
and with a large micropyle, m. Before the contact of the pollen 
with the micropyle, the primary embryo-sac, b, is developed in 
the nucellus. This embryo-sac is at first very small (fig. 1160, 
b), but gradually enlarges (fig. 1161, «), and after a long period 
Fra. 1159. 
Fia. 1160. Bree L612 
Fig. 1159. Pollen of Spruce Fir. 6/. Vesicular protrusions of the extine, e. 
i. The intine, through a rent in which passes the pollen-tube which is 
developed from y, the larger of the two or more cells produced by the 
division of the central cell. g. The smaller cell according to Schacht, 
but merely a slit according to Strasburger. (After Schacht.) Fig. 1160. 
Vertical section of the young unimpregnated ovule of a species of Pinus. 
a. Nucellus containing a smal! primary embryo-sac, 6. m. Micropyle, 
which is here very large. Fig. 1161. Vertical section of an oider ovu e 
of the same. a. Enlarged primary embryo-sae filled with secondary 
endosperm cells, b, within the embryo-sac. c. Two pollen-tubes pene- 
trating the apex of the nucellus. 
becomes filled with delicate cells by free cell-formation, according 
tothe older views, though Strasburger now considers that free 
cell-formation never occurs in embryo-sacs, but that the appear- 
ance of cells and nuclei is due to the division of previously exist- 
ing nuclei. These cells are called endosperm cells ; they disappear 
very soon, and are replaced later on by a fresh development 
(fig. 1161, 6). The following account of the subsequent de- 
velopment of the ovule, and the mode by which it is fertilised, 
is taken from Henfrey, and is founded upon Hofmeister’s in- 
vestigations. 
‘In the upper part of the mass of the last-formed endosperm 
(fig. 1161, 6), from five to eight cells are found to expand more 
than the rest, forming secondary embryo-sacs or corpuscula, 
‘These are not formed in the superficial cells of b, but from 
