Mr. Hassall on the Structure of the Pollen Granule. 105 



tassae produced no result. It is to be remarked, that all those 

 applications which occasioned any motion of the pollen con- 

 tained a greater or less proportion of spirit in them, and that 

 the most volatile liquids, aether and sal volatile, gave rise to the 

 most marked effect. This very obvious motion of the pollen 

 granules is certainly not to be referred to any action of the 

 irritants employed upon them, but to currents in the fluids. 

 That this is the real explanation to be given of the phaeno- 

 menon is satisfactorily proved by the two following facts : 

 1st. If a small quantity of either aether or sal volatile be al- 

 lowed to remain for a few minutes in a watch-glass and the 

 pollen be then added, no motion will follow, the more volatile 

 portion of these liquids having evaporated ; and 2nd, the 

 particles of flour will be equally affected by the applica- 

 tion of the before-mentioned solutions. Water also will some- 

 times cause the emission of the pollen tubes, the principle of 

 endosmosis being called into operation. This emission of the 

 pollen tubes is not the act of an instant, but occupies an ap- 

 preciable time, producing the impression on the mind of some 

 continuous force operating in occasioning it, such as that of 

 endosmosis already referred to. 



The extreme care taken by nature to ensure the fertilization 

 of the seed, a process so essential to the well-being and al- 

 most the existence of man, is very striking, and some of the 

 beautiful provisions by which this important effect is so con- 

 stantly brought about, it is my intention now to notice. First, 

 then, the lining membrane of the anther, as pointed out by 

 Mirbel in 1808, is composed of cellular tissue of a fibrous 

 character, which forms an innumerable quantity of little 

 springs* which are highly elastic, and when dry contract and 

 pull open the valves of the anther, allowing the pollen to 

 escape. This elastic tissue is deprived of its fluid by means 

 of the endosmosis carried on by each individual grain of pol- 

 len, and this exhaustion of its fluid is only completed at the 

 period of the maturity of the pollen. Thus by this unerring 

 contrivance, not alone is the precise period of the opening of 

 the anther, viz. at the perfection of the pollen, provided for 

 and determined on, but it results from it also, that the pollen 

 only should be exposed in the weather most suitable for the 

 performance of its function, that is, in dry weather. The in- 

 jurious effect of a continuance of rain in destroying the ferti- 

 lizing power of the pollen is well known, and is to be ex- 

 plained by the rupture of the granules from the great quan- 

 tity of water imbibed by endosmosis ; and this consequence of 



* This peculiar arrangement of tlic fibres of tlie lining membrane of the 

 anther is very plainly seen in the common nettle. 



