^76 MICROSCOPICAL OBSERVATIONS 



active molecules, so easily separated by pressure from all 

 vegetable tissues, and which are disengaged and become 

 more or less manifest in the incipient decay of semitrans- 

 parent 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 supposed 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 obtained 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 

 ifl primary combinations of the molecules, analogous to 

 those already noticed in mineral bodies and in various 

 organic tissues. 



From the account formerly given of Asclepiadese, Peri- 

 ploceae, and Orchideae, and particularly from what was 

 observed of Asclepiadeae, it is difficult to imagine, in this 

 family at least, that there can be an actual transmission of 

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

 through the processes of the stigma ; and even in these pro- 

 cesses 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 Asclepiadese, the ques- 

 tion respecting 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 con- 

 tact of these particles with the surface of the stigma were 

 necessary to impregnation. 



Finally, it may be remarked that those cases already ad- 

 verted to, in which the apex of the nucleus of the ovulum, 

 the supposed point of impreguatioii, is never brought into 

 contact with the probable channels of fecundation, are more 



