Mr Brown's Microscopical Observations. 337 



The examination of the unimpregnated vegetable Ovulum, an account 

 of which was published early in 1826,* led me to attend more minutely 

 than I had before done to the structure of the Pollen, and to inquire into 

 its mode of action on the Pistillum in Phaenogamous plants. 



In the essay referred to, it was shown that the apex of the 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 pro- 

 bable channels of fecundation ; these being either the surface of the pla- 

 centa, the extremity of the descending processes of the style, or more rarely, 

 a part of the surface of the umbilical cord. It also appeared, however, 

 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 con- 

 veyed 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 Asclepiadeae, 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 attend 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 discer- 

 nible, and that figure not spherical but oblong, I expected, with some con- 

 fidence, to meet with plants in other respects more favourable to the in- 

 quiry, 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 remarkably well adapted to the 

 object in view. 



This plant was Clarckia pulchella, of which the grains of pollen, taken 

 from antherae full grown, but before bursting, were filled with particles or 

 granules of unusually large size, varying from nearly -^^th to about 



ToVo^ of an inc ^ in len g th > and of a figure between cylindrical and ob- 

 long, perhaps slightly flattened, and having rounded and equal extremities. 

 While examining the form of these particles immersed in water, I observ- 

 ed many of them very evidently in motion ; their motion consisting not 



ligingly made for me a simple pocket microscope, having very delicate adjustment and 

 furnished with excellent lenses, two of which are of much higher power than that above- 

 mentioned. To these I have often had recourse and with great advantage, in inves- 

 tigating several minute points. But to give greater consistency to my satements, 

 and to bring the subject as much as possible within the reach of general observation, 

 I continued to employ throughout the whole of the inquiry the same lens with which 

 it was commenced. 



* In the Botanical Appendix to Captain King's Voyages to Australia,) \ol. ii. p. 

 034. et seq. 



