Dr. G. Dickie on the Physiology of Fecundation in Plants. 9 
able satisfactorily to trace them to the ovules. In an appendix, 
however, this opinion is essentially changed, and the direct origin 
_ of these tubes from pollen grains is doubted ; it is also stated that 
in Orchis Morio, Habenaria viridis and Ophrys apifera they were 
traced into the apertures of the ovule. M.Schleiden spoke with 
greater confidence, and described the pollen-tube in the Orchidee 
as entering the foramen of the ovule, its extremity becoming 
converted into the embryo; Meyen expressed himself to the 
same effect, and Link has represented this occurrenee in Gymna- 
denia conopsea. 
That “mucous tubes” are found in connexion with the ovules 
cannot be called in question ; that these are pollen-tubes appears - 
to be not yet satisfactorily proved. 
Such tubes are abundant in Habenaria viridis, and from an ex- 
amination of this plant I have reason to believe, but shall not at 
present positively assert, that the tubes are derived from the 
ovules themselves and not from the pollen. 
The ovule in the Orchidee is of exceedingly simple structure ; 
a nucleus, at first partially, afterwards entirely covered by a 
single membrane, the two becoming ultimately so fused together 
that the testa appears composed of one layer only. Mr. Brown, 
in the essay already quoted, states that soon after this change a 
minute opake body makes its appearance about the middle of the 
cavity of the testa ; he also traced a jointed thread from its apex 
nearly to the open end of the testa. This thread, with its dilated 
extremity, Meyen and Schleiden have mistaken for a pollen-tube. 
Mr. Brown very accurately describes this thread as consisting of 
a simple series of short cells, “ the lowest cell being probably the 
original state of what afterwards becomes the embryo.” I be- 
heve that a prolongation of the uppermost cell of this thread, 
beyond the opening of the testa, accounts for the presence of the 
mucous tubes so abundant upon the placenta. The appearances 
described can be readily seen in Habenaria viridis, and the simple 
cellular structure of the embryo, even when nearly mature, is evi- 
dent in Goodyera repens. The jomted thread in Habenaria viri- 
dis is at first straight, and the cells composing it have a firm ad- 
hesion to each other ; when the lowest cell (the embryo) has at- 
tained considerable size and is nearly mature, the cord which 
issues from the mouth of the ovule breaks off at some joint near — 
this opening ; the rupture is preceded by an evident change in 
the mutual position and connexion of the cells, the whole cord 
‘becomes tortuous, the points of adhesion of the cells diminish in 
extent, and the joints easily separate from each other. Even in 
seeds to all appearance fully ripe I have seen the thread broken 
off at the mouth of the testa, while the remaining cells were still 
