162 Mr. R. Brown on the Existence of active Molecules 



nucleus of the Ovulum, the point which is universally the seat 

 of the future Embryo, was very generally brought into contact 

 with the terminations of the probable channels of fecundation; 

 these being either the surface of the placenta, the extremity of 

 the descending processes of the style, or more rarely, a part 

 of the surface of the umbilical cord. It also appeared, how- 

 ever, from some of the facts noticed in the same Essay, that 

 there were cases in which the Particles contained in the grains 

 of pollen could hardly be conveyed to that point of the ovulum 

 through the vessels or cellular tissue of the ovarium ; and the 

 knowledge of these cases, as well as of the structure and 

 economy of the antherae in Asclepiadece, had led me to doubt 

 the correctness of observations made by Stiles and Gleichen 

 upwards of sixty years ago, as well as of some very recent 

 statements, respecting the mode of action of the pollen in the 

 process of impregnation. 



It was not until late in the autumn of 1826 that I could at- 

 tend to this subject ; and the season was too far advanced to 

 enable me to pursue the investigation. Finding, however, in 

 one of the few plants then examined, the figure of the particles 

 contained in the grains of pollen clearly discernible, and that 

 figure not spherical but oblong, I expected, with some confi- 

 dence, to meet with plants in other respects more favourable 

 to the inquiry, in which these particles, from peculiarity of 

 form, might be traced through their whole course : and thus, 

 perhaps, the question determined whether they in any case 

 reach the apex of the ovulum, or whether their direct action 

 is limited to other parts of the female organ. 



My inquiry on this point was commenced in June 1827, 

 and the first plant examined proved in some respects remark- 

 ably well adapted to the object in view. 



This plant was Clarckia pulchella, of which the grains of 

 pollen, taken from antherse full grown, but before bursting, were 

 filled with particles or granules of unusually large size, vary- 

 ing from nearly ¥I ^ n th to about j^Wth of an inch in length, 

 and of a figure between cylindrical and oblong, perhaps 

 slightly flattened, and having rounded and equal extremities. 

 While examining the form of these particles immersed in wa- 

 ter, I observed many of them very evidently in motion ; their 

 motion consisting not only of a change of place in the fluid, ma- 

 nifested by alterations in their relative positions, but also not 

 unfrequently of a change of form in the particle itself; a con- 

 traction or curvature taking place repeatedly about the middle 

 of one side, accompanied by a corresponding swelling or con- 

 vexity on the opposite side of the particle. In a few in- 

 stances the particle was seen to turn on its longer axis. These 

 motions were such as to satisfy me, after frequently repeated ob- 

 servation, 



