102 M. Raspairs experiments on the granules of Pollen 



ches of this kind require^ and the importance which ought to be 

 attached to what is called the use of expensive miroscopes.* 



1. I have already proved, in my memoir on organic tissues, 

 that the pollens of different plants vary in the quantity of resi- 

 nous and volatile substances which they contain. It would, 

 therefore, not be surprising, if in using any other pollen than 

 that of the Malvaceae, we should not find so many globules so- 

 luble in alcohol. 



2. In order to recognize the chemical nature of the globules 

 discharged by the explosion, we must not pour the alcohol on 

 the object-plate before the evaporation of the water, for in that 

 case nothing would be dissolved, since the alcohol would ex- 

 tend itself over the water instead of dissolving the resin. 



3. If we wish to stop the movements arising from the eva- 

 poration of the water, or of the volatile substances with which 

 it is impregnated during the explosion of the grain of pollen, 

 we must not content ourselves with covering the water with a 

 film of mica, for the sides of the film being always unevenly 

 applied against the object-plate, would not prevent evaporation 

 at the edges, which would become a still more pow^erful cause 

 of illusory motions and currents, than if the evaporation con- 

 tinued to be carried on over the whole surface. 



We ought to make use of two plates of glass ground upon 

 one another, and one of which has a cavity of the form of a 

 spherical segment. We have then only to put a number of 

 grains of pollen in the cavity, and after passing water over it, 

 to slide quickly the one plate over the other. The explosion 

 of the grains of pollen will at first impress a general motion on 

 the globules, but the granules will soon resume the immobility 

 which characterizes them. 



4. It may perhaps be objected, that observations opposite to 

 these, on the animality or the mobility of the granules of pol- 

 len, have been made with a microscope superior to mine, and 



• A celebrated astronomer (See ie G7oZ>e for July) has publicly declar- 

 ed that cateris paribus the microscope of Amici is superior to every other 

 microscope, which must mean that the prism which distinguishes it from 

 others adds to the light and the magnifying power. He afterwards laid it 

 down as a principle, that the value of microscopical observations was in the 

 direct ratio of the intrinsic value and the superiority of microscopes. 



