ON ACTIVE MOLECULES. 407 



tlie particle itself; a contraction or cnrvaturc taking place 

 repeatedly abont the middle of one side, accompanied by a 

 corresponding swelling or convexity on the opposite side of 

 the particle. In a few instances the particle was seen to 

 tnrn on its longer axis. These motions were such as to 

 satisfy me, after frequently repeated observation, that they 

 arose neither from currents in the fluid, nor from its r^ 

 gradual evaporation, but belonged to the particle itself. 



Grains of pollen of the same plant taken from antherae 

 immediately after bursting, contained similar subcylin- 

 drical particles, in reduced numbers, however, and mixed 

 with other particles, at least as numerous, of much smaller 

 size, apparently spherical, and in rapid oscillatory motion. 



These smaller particles, or Molecules as I shall term 

 them, when first seen, I considered to be some of the cylin- 

 drical particles swimming vertically in the fluid. But 

 frequent and careful examination lessened my confidence 

 in this supposition ; and on continuing to observe them 

 until the water had entirely evaporated, both the cylindrical 

 particles and spherical molecules were found on the stage 

 of the microscope. 



In extending my observations to many other plants of the 

 same natural family, namely OnagraricB, the same general 

 form and similar motions of particles were ascertained to 

 exist, especially in the various species of Oenothera, which I 

 examined. I found also in their grains of pollen taken from 

 the anthera} immediately after bursting, a manifest reduc- 

 tion in the proportion of the cylindrical or oblong particles, 

 and a corresponding increase in that of the molecules, in a 

 less remarkable degree, however, than in Clarckia. 



This appearance, or rather the great increase in the num- 

 ber of the molecules, and the reduction in that of the cylin- 

 drical ])articles, before the grain of pollen could possibly 

 have come in contact with the stigma, — were perplexing 

 circumstances in this stage of the inquiry, and certainly not 

 favorable to the supposition of the cylindrical particles act- 

 ing directly on the ovuhun ; an opinion which 1 was inclined 

 to adopt when I first saw them in motion. These circum- 

 stances, however, induced me to multiply my observations. 



