ON ACTIVE MOLECULES. 469 



In Periplocece, and in a few ApocinecBy the pollen, which 

 in these plants is se{)ara])le into coniponnd grains filled with 

 spherical moving particles, is applied to processes of the 

 stigma, analogons to those of Asclepiadeae. A similar eco- 

 nomy exists in Orchidcce, in which tiie pollen masses are 

 always, at least in the early stage, granular ; the grains, 

 whether simple or compound, containing niinute, nearly 

 spherical particles, but the whole mass being, with [7 

 very few exceptions, connected by a determinate point of 

 its surface with the stigma, or a glandular process of that 

 organ. 



Having found motion in the particles of the pollen of 

 all the living plants which I had exannned, I was led next 

 to inquire whether this property continued after the death 

 of the i)lant, and for what length of time it was retained. 



In plants, either dried or immersed in spirit for a few 

 days only, the particles of pollen of both kinds were found 

 in motion equally evident with that observed in the living 

 plant ; specimens of several plants, some of which had been 

 dried and preserved in an herbarium for upwards of twenty- 

 years, and others not less than a century, still exhibited the 

 molecules or smaller spherical particles in considerable 

 numbers, and in evident motion, along with a few of the 

 larger particles, whose motions were much less manifest, 

 and in some cases not observable.^ 



In this stage of the investigation having found, as I be- 

 lieved, a peculiar character in the motions of the particles 

 of pollen in water, it occurred to me to appeal to 

 this peculiarity as a test in certain flimilies of Crypto- 

 gamous plants, namely, Mosses, and the genus Equisetum, 



' "Wliilefliis sheet was passing through tlie press I have examined the pollen 

 of several flowers which iiave been immersed in weak spirit about eleven 

 nionlhs, |)aiticularly of yiula tricolor^ Zizauia aquatica^ and Zea Mays ; and in 

 all these plants the peculiar particles of the pollen, which arc oval or &hort ob- 

 long, though somewhat reduced in number, retain their form pcrfecily, and 

 exhibit evident motion, though I think not so vivid as in those belonging to 

 the living plant. In Viola triculur, in which, as well as in otlit-r species of I he 

 same natural section of the genus, the j)ollen has a very remarkable form, the 

 grain on immersion in nitric acid still di.scharged its contents by its four angles, 

 though with less force than in the recent plant. 



