728 Ml'. 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. 



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 



