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 542 ON THE ORGANS AND MODE OF FECUNDATION

as a continuation of the tissue of the stigma and style, and as existing before the apphcation of the pollen to the female organ.

And 3rdly, He supposes that the male influence reaches the ovula in Orchidese before the inversion of the nucleus ; an opinion founded, as it seems, on his observations on Epipactis, in which, as well as in some other genera of the order, this is the state of the ovulum in the expanded flower.

In AscLEPiADEiE M. Brougniart's observations, made chiefly in Asdepias amcena and Gomjyhocarjms fruticosa, accord with my statements as far as relates to the applica- 745] tion of the more convex edge of the pollen mass to the base of the stigma, its consequent dehiscence, the protrusion of the pollen tubes, and their penetration into the cavity of the style.

The chief differences are,

1st, His not even suspecting the agency of insects in the fecundation of this family, and particularly in the plants examined by him, in which I have regarded their assist- ance as absolutely necessary.

2ndly, In his assuming that the pollen mass in these two genera of Asclepiadeae is ruptured, and comes in con- tact with the base of the stigma without leaving the cell of the anthera.

3rdly, His conjecturing that the secretion visible in the expanded flower on the angles of the stigma after removing the glands, is absorbed by the glands and conveyed through their arms or processes to the pollen mass, which it excites to the production of pollen tubes.

��Dr. Ehrenberg, on the subject of Asclepiadeae, repeats, with some slight modifications, his former statements quoted in my paper, and illustrates them by figures. In addition, he suspects that the pollen masses (which with Professor Link he regards as the true anthera, and the cells in which they are lodged as processes of the perigo- nium), are not originally distinct from the glands of the

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