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 534 ON THE ORGANS AND MODE OF FECUNDATION

��734] EXPLANATION OF THE PLATES.

��Tab. 30 (3i). Asclepias purpurascens.

Fig. 1. A brancli in flower: — natural size.

Eig. 2. An expanded flower, of which two of the foliola coronas and one of the antlierse are removed: — moderately magnified.

Fig. 3. A front or inner view of an anthera, to show the extent of bursting, particularly with relation to the pollen mass, of which the greater part is included in the non-dehiscent portion: — magnified as fig. 2.

Fig. 4. A pollen mass, more highly magnified, separated from its gland and arm, and divided transversely, to show its cellular structure (first discovered in Asclepias curassavica in 1805 by Mr. Bauer), with grains of pollen, their granules, and some drops of an oily fluid.

Fig. 5. A pollen mass entire, with a small portion of the arm adhering to its apex: — magnified as fig. 4.

Fig. 6. A transverse section of a pollen mass, still more highly magnified, in one of the cells of which is seen the single grain (or inner membrane), also separately exhibited to show that it is simple and slightly angular.

Fig. 7. The pistillum with pollen masses, that have burst and protruded their tubes, applied to the base of the stigma, the glands and their arms being removed. The cords formed by the pollen tubes have passed along the corresponding sides of the conical base of the stigma, and have reached the tops of the styles.

Fig. 8. A longitudinal section (more highly magnified) of the conical base of the Stigma with the tw^o styles, to show more distinctly the course of the pollen tubes.

735] Y\^. 9. A pollen mass after bursting, with its cord formed of the pollen tubes, entering the apex of the style, which is there lacerated.

Fig. 10. The two Ovaria with their styles, one being somewhat enlarged in consequence of impregnation, and opened longitudinally; exhibiting pollen tubes extending from the apex of the style to the commencement of the placenta,

Fig. 11. The same two ovaria and styles, both opened, to show that in one (the left), which is somewhat smaller, no pollen tubes are contained; the other (the right), which is impregnated, shows the tubes reaching the ovula, but not extending further.

Fig. 12. Two grains of pollen (or rather grains deprived of their outer membranes), with portions of their tubes and contained spheroidal granules; proving that the tubes are extensions of this (the inner) membrane; — very highly magnified.

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