EMBRYO-SAC OF GYMNADENTA CONOPSEA. 
7 
act of fertilisation ; the pollen-tube, after a sinuous course 
from the placenta, has made a sharp bend ere plunging into 
the micropyle, and has then spread its broad apex over the 
Gehiilfinnen,” apparently penetrating between the sac and 
integument, but the difficulty of tracing so delicate an out- 
line as it here presents is no ordinary one.* It does not 
break through the top of the sac, but the well-marked 
contour of the latter is to be seen through the transparent 
tube, the walls of which are here marked by delicate longi- 
tudinal striations, which appear to be folds, either caused by 
contraction from reagents, or the closing in of the inner 
integument ; I cannot identify it with the filiform apparatus 
of Schacht, since it is on the pollen-tube, and has nothing 
whatever to do with the embryo-sac contents. In the course 
of the tube are developed the peculiar cellulose blocks pro- 
jecting inwards from its walls, and serving apparently to 
shut off the contents of the tube as it grows ; these “ Propfen 
or stoppers were described by Strasburger^ and Elfving,^ and 
occur in such quantities that a cross section of the pollen- 
tube bundles appears marked here and there by waxy- 
looking drops interspersed among silvery-like cellular walls 
of the tubes. In the figure is one of these stoppers repre- 
sented as it occurred in the tube just ere the final bend. 
The outline of the embryo-sac is still marked by the 
remains of the nucleus-cells which it compressed and des- 
troyed in its growth, but the cap-cells appear to have quite 
disappeared ; even the latter, however, persist for a long time 
(cf. figs. 6 — 13) as a refractive cap on the apex of the sac, in 
some cases (fig. 12) presenting a conical, or even beaked 
appearance. If no pollen-tube enters the micropyle, the 
whole ovule turns brown, shrivels, and the contents of the 
sac become ill defined and decay ; the egg- cell persists 
apparently longer than the Gehulfinnen (fig. 17, a). In all 
these cases, and up to a much later period, we find the 
remaining cells of the central or axial row persist beneath 
the sac ; in fact, the air space already referred to is formed 
beneath the lower one, and between it and the outer integu- 
ment when the sharp bend is established. 
The fact that the oosphere is fertilised is marked by the^ 
appearance of a thin cellulose coat around it; it elongates, 
and its nucleus prepares to divide. The contents of the Gehul- 
finnen and other parts of the sac, on the contrary, become 
* Ilofmeisler represents the tube as entering the sac in Orc/a's morio. 
‘ Vergl. Unters.,’ t. iv. 
^ Loc. cit. 
* ‘ Jtnaischer Zcitschr. fiir Naiurwisscnsch,’ 1878 . 
