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 Orchidece 

 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 occurrence 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 Orchidece 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- 

 lieve 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 jointed 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 



