ALDRIDGE ON POLLEN. 93 



of the Starch becomes precipitated. The latter method is 

 much to be preferred when it is sougiit to ascertain the exist- 

 ence of starch, as the observation of a very small quantity 

 often fails by the first method. That the grains coloured 

 blue are actual starch, is placed beyond doubt, by the diluted 

 acid and iodine producing analogous appearances with the 

 starch contained in other organs. 



The little oil-drops and grains of starch constitute the so- 

 called grannies of the pollen, wl)ich in late times have become 

 the object of different inquiries. These are the particles in 

 which special motions were formerly pointed out, and this 

 erroneous observation, caused an infusorial organization to 

 be assigned to these granules, and they were called the sper- 

 matozoae of plants. So extreme was our ignorance, that at 

 the most, out of a little particle completely unorganized, 

 imagination called into existence a new being, in which, 

 motions having been perceived, we at once drew a compari- 

 son between the fovilla-grains and natural infusoria, of the 

 smaller of which we as yet know nothing except their move- 

 ments. Through R. Brown's discovery of the molecular 

 motions, the motions of the granules, independent of infuso- 

 rial life, was demonstrated to be possible, and the determina- 

 tion of their chemical properties at present, places them wholly 

 in the category of molecular motions. However, both R. 

 Brown, and Adolphe Brongniart, have described in the 

 fovilla grains of higher vegetables, besides a change of place 

 also a change of form, which they consider as an indication 

 of a life-activity, and one of the strongest arguments for their 

 comparison with spermatozoae. The author considers this 

 apparent change of form to be partly illusory, and partly 

 produced by the streaming of the oil-drops. 



Having thus described the constituents of the contents of 

 the pollen, the author proceeds to treat of the membrane of 

 this organ. The envelope, by which, in all plants without 

 exception, the fovilla is surrounded, he divides into two kinds 

 of membrane, one a simple membrane, and the other a skin 

 of a compound construction. All plants do not possess both 



