LINNEAN SOCIETY OF LONDON. 63 



various plants, and the order of their reduction in relation to 

 other parts of the flower. 



In 1828 Brown printed for private circulation a Memoir 

 which attracted a great deal of attention, entitled " A brief 

 account of Microscopical Observations made in the months of July, 

 August, and September, 1827, on the Particles contained in the 

 Pollen of Plants ; and on the general Existence of Active Mole- 

 cules in Organic and Inorganic bodies ; " and in the following 

 year " Additional Observations on Active Molecules." For 

 reasons that will afterwards appear, it is very difficult to give a 

 clear account of this curious investigation. Brown states that the 

 research was suggested by his desire to study, more minutely than 

 he had done, the structure of pollen, and to inquire into its mode 

 of action on the pistillum. The pollen he commenced with 

 was that of Clarkia pulchella, in which, when immersed in 

 water, he detected particles of two kinds, both exhibiting motion. 

 In the pollen-grains taken from the undehisced anther of this 

 plant he observed only particles of unusually large size, of a figure 

 between cyliudric and oblong, which had motions both of change 

 of position and of form ; but in the case of pollen-grains of the 

 same plant taken from the anther after it had dehisced, he found, 

 mixed with a reduced number of the same large moving particles, 

 other particles at least as numerous, of a spherical form, and in 

 rapid rotatory motion. These smaller particles he designated 

 molecules, to distinguish them from the larger. Extending his 

 observations to many other plants of the same Natural Order as 

 Clarkia, he found the same phenomena in all. The pollen of 

 many species of the more important and remarkable orders of 

 Phanerogams was then subjected to examination, always with the 

 result that they contained particles in motion, but with modifi- 

 cations. From polleu, Brown proceeded to the examination of 

 other vegetable tissues, living, dead, and dried (even that of mosses 

 that had been dried for upwards of 100 years), with the result 

 that when these were reduced to the condition of minute particles, 

 and floated in water, they invariably exhibited motion. Amongst 

 other bodies, he examined the " cylindrical anther or pollen " of 

 Mosses ; he does not say whether these were in a living or dead 

 state; if the formei", he narrowly escaped being the discoverer of 

 the Antherozoids of plants. 



It is needless to carry further the history of Brown's inde- 

 fatigable endeavours to fiud in the motion within the pollen 

 the " test of the male organ," of which he was in quest : his 

 sagacity must soon have led him to perceive that the motions 

 which he had detected, or some of them, were physical. Pur- 

 suing the inquiry into inorganic substances, of which he examined 

 an enormous number, using many methods of demonstrating that 

 the motions were independent of evaporation, currents of the 

 fluid in which the particles were immersed, or other external 

 conditions, he at length established the fact of that oscillatory 



