128 Mr. Brown on the Organs and Mode of 
from the prominent point of the edge to every other part of the 
surface of the covering itself. 
To ascertain whether contact of the convex edge of the pollen 
mass with this point of the stigma was 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 position 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 ex- 
posed, 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 slowly 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. i 
Pollen masses of Asclepias purpurascens being applied to the 
stigma of Epipactis palustris, and immersed in its viscid secre- 
tion, the dehiscence, contrary to expectation, not only took 
place, but even more speedily than usual, that 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. phytolaccoides, 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, so to speak, of its mass, 
which in some cases produced its tubes merely on continued 
immersion in water. I even found that in this species, in the 
_ gradual 
