550 srPPLEMFA'TARY OBSERVATIOXS 



proceeding from it is continued, though not very distinctly, 

 to the opposite or lo\ver extremity. On the upper and 

 broader end of the Ovulum a deep groove is observable, 

 commencing at its inner margin, which is nearly in contact 

 with the Placenta, and extending through its whole 

 breadth, and somewhat obHquely downwards, so as to 

 terminate at the same height on the outer side of the 

 Ovulum with the upper edge of the ventral umbilical cord. 

 This groove, or that point of it to which the Pollen tube is 

 attached, occupies the place of the Foramen so generally 

 found in the unimpregnated ovidum of Phsenogamous 

 plants. In Asclejjias phi/iolaccoides, however, and I believe 

 the observation may be extended to every species of the 

 genus, there is certainly no perforation, nor at this period 

 are the coats and nucleus of the Ovulum separable or even 

 distinguishable ; and the same apparent simplicity of struc- 

 ture is found even in its earher stages. 



Soon after the Pollen tubes enter the cavity of the 

 Ovarium, even before the Corolla falls off, they may be 

 found spread over the whole ovuliferous surface of the 

 Placenta, which then often becomes of a light brown colour, 

 but never dark brown or black, like the tipper non- 

 ovuliferous portion. From the surface of the Placenta 

 the Tubes go off, one to each Ovulum, along the depressed 

 apex of which the Tube passes till it reaches the outer 

 extremity of the groove, where it is invariably inserted. 

 To this point the Tube adheres so firmly, that I am in- 

 clined to think it actually penetrates, to some depth at 

 ^] least into the substance of the Ovulum ; a fact, however, 

 which I have not yet absolutely ascertained. 



Soon after the insertion of the Pollen tube, a change 

 takes place in the appearance of the Ovulum, an internal 

 body or nucleus becoming visible, with the upper attenuated 

 extremity of which the point of insertion accurately corre- 

 sponds. 



The Pohen tube, when thus inserted into the Ovulum, is 

 not always absolutely destitute of granules ; in some cases 

 containing a few, which in size and form seem to be iden- 

 tical with those that completely fill it in its nascent state. 



