344? Analysis of Scientific Books and Memoirs. 



which is in part founded on the partial withering confined 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 active mole- 

 cules, so easily separated by pressure from all vegetable tissues, and which 

 are disengaged and become more or less manifest in the incipient decay of 

 semitransparent parts, it would not be difficult to trace granules through 

 the whole length of the style : and as these granules are not always visible 

 in the early and entire state of the organ, they would naturally be sup- 

 posed to be derived from the pollen, in those cases at least in which its 

 contained particles are not remarkably different in size and form from the 

 molecule. 



It is necessary also to observe that in many, perhaps I might say in most 

 plants, in addition to the molecules separable from the stigma and style 

 before the application of the pollen, other granules of greater size are ob- 

 tained by pressure, which in some cases closely resemble the particles of 

 the pollen in the same plants, and in a few cases even exceed them in size: 

 these particles may be considered as primary combinations of the mole- 

 cules, analogous to those already noticed in mineral bodies and in various 

 organic tissues. 



From the account formerly given of Asclepiadeae, Periplocere, and Or- 

 chidete, and particularly from what was observed of Asclepiadeae, it is dif- 

 ficult to imagine, in this family at least, that there can be an actual trans- 

 mission of particles from the mass of pollen, which does not burst, through 

 the processes of the stigma ; and even in these processes I have never been 

 able to observe them, though they are in general sufficiently transparent 

 to show the particles were they present. But if this be a correct statement 

 of the structure of the sexual organs in Asclepiadeae, the question respect- 

 ing this family would no longer be, whether the particles in the pollen 

 were transmitted through the stigma and style to the ovula, but rather 

 whether even actual contact of these particles with the surface of the stig- 

 ma were necessary to impregnation. 



Finally, it may be remarked that those cases already adverted to, in 

 which the apex of the nucleus of the ovulum, the supposed point of im- 

 pregnation, is never brought into contact with the probable channels of 

 fecundation, are more unfavourable to the opinion of the transmission of 

 the particles of the pollen to the ovulum, than to that which considers 

 the direct action of these particles as confined to the external parts of the 

 female organ. 



The observations, of which I have now given a brief account, were made 

 in the months of June, July, and August 1827. 



The facts ascertained respecting the motion of the particles of the pollen 

 were never considered by me as wholly original ; this motion having, as I 

 knew, been obscurely seen by Needham, and distinctly by Gleichen, who 

 not only observed the motion of the particles in water after the bursting 

 of the pollen, but in several cases remarked their change of place within 

 the entire grain. He has not, however, given any satisfactory account 



