528 ON THE ORGANS AND MODE OF FECUNDATION
and applied to the prominent point of the convex edge of the pollen mass, producing its appropriate action not only in those cells or grains of pollen in immediate contact with that point, but generally in every grain in the mass. But as there are no visible conductors of this stimulus within the mass, it must either be supposed to be propagated from one cell to another, or conveyed from the prominent l7;:s point of the edge to every other part of the surface of the covering itself.
To ascertain whether contact of the convex edo-e of the pollen mass with this point of the stigma Avas absolutely necessary for the rupture of the mass and the production of tubes, I in the first place introduced a mass into the fissure, but with its convex edge outwards. In this posi- tion no change whatever took place.
I next removed one of the glands of the angles of the stigma, and applied the convex edge of a mass to the surface thus exposed, which even in this stage — to facilitate the removal of the gland by insects — continues to secrete. In this case, dehiscence and protrusion of pollen tubes did follow, more slowdy, however, and less completely, than when brought in contact with the non-secreting base.
On applying the pollen mass of one species of Asclepias to the base of the stigma of another, the usual changes generally took place ; but still, as it seemed, less perfectly, and only after a longer interval.
Pollen masses Q>i Asclepias 'joiiypurascens being applied to the stigma of Ejnjjacfis palustris, and immersed in its viscid secretion, the dehiscence, contrary to expectation, not only took place, but even more speedily than usual, tliat is within twenty-four hours. Some of the grains were also found discharged from the mass unchanged, while others, both discharged and still inclosed, had begun to produce tubes.
The greater number of these observations were also made with A. p)Jf^^oJaccoides, which, on account of the greater size of its flower, I at first preferred. I found, however, with reference to such experiments, an objection to employing this species, arising from the great excitability,
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