3S8 Analysis of Scientific Books and Memoirs. 



only of a change of place in the fluid, manifested by alterations in their 

 relative positions, but also not unfrequently of a change of form in the par- 

 ticle itself ; a contraction or curvature taking place repeatedly about the 

 middle of one side, accompanied by a corresponding swelling or convexity 

 on the opposite side of the particle. In a few instances the particle was 

 seen to turn on its longer axis. These motions were such as to satisfy me, 

 after frequently repeated observation, that they arose neither from currents 

 in the fluid, nor from its gradual evaporation, but belonged to the particle 

 itself. 



Grains of pollen of the same plant taken from antherse immediately after 

 bursting, contained similar subcylindrical particles, in reduced numbers, 

 however, and mixed with other particles, at least as numerous, of much 

 smaller size, apparently spherical, and in rapid oscillatory motion. 



These smaller particles, or molecules as I shall term them, when first 

 seen, I considered to be some of the cylindrical particles swimming verti- 

 cally in the fluid. But frequent and careful examination lessened my con- 

 fidence in this supposition ; and on continuing to observe them until the 

 water had entirely evaporated, both the cylindrical particles and spherical 

 molecules were found on the stage of the microscope. 



In extending my observations to many other plants of the same natural 

 family, namely Onagrarice, the same general form and similar motions of 

 particles were ascertained to exist, especially in the various species of (Eno- 

 thera, which I examined. I found also in their grains of pollen taken 

 from the anthera? immediately after bursting, a manifest reduction in the 

 proportion of the cylindrical or oblong particles, and a corresponding in- 

 crease in that of the molecules, m a less remarkable degree, however, than 

 in Clarckia. 



This appearance, or rather the great increase in the number of the mole- 

 cules, and the reduction in that of the cylindrical particles, before the grain 

 of pollen could possibly have come in contact with the stigma, — were per- 

 plexing circumstances in this stage of the inquiry, and certainly not favour- 

 able to the supposition of the cylindrical particles acting directly on the 

 ovulum ; an opinion which I was inclined to adopt when I first saw them 

 in motion. I hese circumstances, however, induced me to multiply my 

 observations, and I accordingly examined numerous species of many of the 

 more important and remarkable families of the two great primary divisions 

 of Phsenogamous plants. 



In all these plants particles were found, which in the different families 

 or genera varied in form from oblong to spherical, having manifest motions 

 similar to those already described ; except that the change of form in the 

 oval and oblong particles was generally less obvious than in Onagrariac, 

 and in the spherical particle was in no degree observable*. In a great pro- 

 portion of these plants I also remarked the same reduction of the larger 

 particles, and a corresponding increase of the molecules after the bursting 



* In Lolium jperenne, however, which I have more recently examined, though the 

 particle was oval and of smaller size than in Onagraria:, this change of form was at 

 least as remarkable, consisting in an equal contraction in the middle of each side, 

 so as to divide it into two nearly orbicular portions. 



