550 s r pr LE >f i-: n t a r y o r. s e r v a t ions
proceeding from it is continued, though not very distinctly, to the opposite oi* lower 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 someAvhat obliquely dowmwards, 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 ovulum of Phsenogamous ])lants. In Asclejnas phi/lolaccoides, how^ever, 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 earlier 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 brovrn colour, but never dark ])rown or black, like the upper non- ovuliferous portion. Prom 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 t] least into the substance of the Ovulum ; a fact, hoAvever, 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 visil)le, with the upper attenuated extremity of which the point of insertion accurately corre- sponds.
The Pollen 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.
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