172 Mr. R. Brown on the Existence of active Molecules. 



before the Academy of Sciences of Paris, and has since pub- 

 lished in the Annates des Sciences Naturelles. 



Neither in the abstract referred to, nor in the body of the 

 memoir, which M. Brongniart has with great candour given 

 in its original state, are there any observations, appearing of 

 importance even to the author himself, on the motion or form 

 of the particles ; and the attempt to trace these particles to 

 the ovulum, with so imperfect a knowledge of their distinguish- 

 ing characters, could hardly be expected to prove satisfactory. 

 Late in the autumn of 1 827, however, M. Brongniart having 

 at his command a microscope constructed by Amici, the cele- 

 brated professor of Modena, he was enabled to ascertain many 

 important facts on both these points, the result of which he 

 has given in the notes annexed to his memoir. On the general 

 accuracy of his observations on the motions, form, and size of 

 the granules, as he terms the particles, I place great reliance. 

 But in attempting to trace these particles through their 

 whole course, he has overlooked two points of the greatest 

 importance in the investigation. 



For, in the first place, he was evidently unacquainted with 

 the fact, that the active spherical molecules generally exist in 

 the grain of pollen along with its proper particles ; nor does it 

 appear from any part of his memoir that he was aware of the 

 existence of molecules having spontaneous or inherent mo- 

 tion, and distinct from the peculiar particles of the pollen, 

 though he has doubtless seen them, and in some cases, as it 

 seems to me, described them as those particles. 



Secondly, he has been satisfied with the external appearance 

 of the parts in coming to his conclusion, that no particles capa- 

 ble of motion e'xist in the style or stigma before impregnation. 



That both simple molecules and larger particles of diffe- 

 rent form, and equally capable of motion, do exist in these 

 parts, before the application of the pollen to the stigma can 

 possibly take place, in many of the plants submitted by him 

 to examination, may easily be ascertained ; particularly in An- 

 tirrhinum majus, of which he has given a figure in a more ad- 

 vanced state, representing these molecules or particles, which 

 he supposes to have been derived from the grains of pollen, 

 adhering to the stigma. 



There are some other points respecting the grains of pollen 

 and their contained particles in which I also differ from M. 

 Brongniart, namely, in his supposition that the particles are 

 not formed in the grain itself, but in the, cavity of the an- 

 thera ; in his assertion respecting the presence of pores on 

 the surface of the grain in its early state, through which the 

 particles formed in the anthera, pass into its cavity ; and lastly, 



on 



