ON ACTIVE MOLECULES. 475 



sliall I hazard any conjectures whatever respecting these 

 molecules, which appear to be of such general existence in 

 inorganic as well as in organic bodies ; and it is only further 

 necessary to mention the principal substances from which I 

 have not been able to obtain them. These are oil, resin, 

 wax and sulphur, such of the metals as I could not reduce 

 to that minute state of division necessary for their separation, 

 and finallv, bodies soluble in water. 



In returning to the subject with which my investigation 

 commenced, and which was indeed the only object I originally 

 had in view, I had still to examine into the probable mode 

 of action of the larger or peculiar particles of the pollen, 

 which, though in many cases diminished in number before 

 the grain could possibly have been applied to the stigma, 

 and particularly in Clarckia, the plant first examined, were 

 yet in many other plants found in less diminished propor- [is 

 tion, and might in nearly all cases be supposed to exist in 

 sufficient quantity to form the essential agents in the process 

 of fecundation. 



I was now therefore to inquire, whether their action was 

 confined to the external organ, or whether it were possible 

 to follow them to the nucleus of the ovulum itself. My 

 endeavours, however, to trace them through the tissue of 

 the style in plants well suited for this investigation, both 

 from the size and form of the particles, and the development 

 of the female parts, particularly Onagrarise, was not attended 

 with success ; and neither in this nor in any other tribe 

 examined, have I ever been able to find them in any part of 

 the female organ except the stigma. Even in those famihes 

 in which I have supposed the ovulum to be naked, namely, 

 Cycadese and Coniferae, I am inclined to think that the 

 direct action of these particles, or of the pollen containing 

 them, is exerted rather on the orifice of the proper mem- 

 brane than on the apex of the included nucleus ; an opinion 

 which is in part founded on the partial withering con- 

 fined to one side of the orifice of that membrane in the 

 larch, — an appearance which I have remarked for several 

 years. 



To observers not aware of the existence of the elementary 



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