Mr Brown's Microscopical Observations. 345 



either of the forms or of the motions of these particles, and in some cases 

 appears to have confounded them with the elementary molecule, whose 

 existence he was not aware of. 



Before I engaged in the inquiry in 1827, I was acquainted only with 

 the abstract given by M. Adolphe Brongniart himself, of a very elaborate 

 and valuable memoir, entitled " Recherches sur le Generation et le Drve- 

 loppernent del Embryon dans les Vegetaux Pkanerogames" which he had 

 then read before the Academy of Sciences of Paris, and has since published 

 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 parti- 

 cles to the ovulum with so imperfect a knowledge of their distinguishing 

 characters, could hardly be expected to prove satisfactory. Late in the 

 autumn of 1827, however, M. Brongniart having at his command a micro- 

 scope constructed by Amici, the celebrated 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 gene- 

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

 granules, as he terms the particles, I place great reliance. But in attempt- 

 ing 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 sponta- 

 neous or inherent motion, 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 capable of motion exist in the 

 style or stigma before impregnation. 



That both simple molecules and larger particles of different 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 Antirrhinum mqjus, of which he has given a figure in a more advanced 

 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 anthera ; 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 the existence of 



