ON ACTIVE MOLECULES. 469 



In Periplocea, and in a few Apocinea, the pollen, which 

 in these plants is separable into compound grains filled with 

 spherical moving particles, is applied to processes of the 

 stigma, analogous to those of Asclepiadese. A similar eco- 

 nomy exists in Orchideos, in which the pollen masses are 

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

 whether simple or compound, containing minute, nearly 

 spherical particles, but the' whole mass being, with n 

 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 examined, I was led next 

 to inquire whether this property continued after the death 

 of the plant, 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 raq to appeal to 

 this peculiarity as a test in certain faniilies of Crypto- 

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



' While tliis sheet was passing tlirough the press I have examined the pollen 

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

 months, particularly of Viola, tricolor, Zizania aquatica, and Zea Mays ; and in 

 all these plants the peculiar particles of the pollen, which are oval or short ob- 

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

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

 the living plant. In Viola tricolor, in which, as well as in other species of the 

 same natural section of the genus, the pollen has a very remarkable form, the 

 grain on immersion in nitric acid still discharged its contents by its four angles, 

 though with less force than in the recent plant. 



