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



pass along the surface of glass. Again, the internal mem- 

 brane of the pollen grain of Strelitzia humilis, when denuded 

 of the extine, presents a cellular appearance, which is owing 

 to the presence of numerous globules of various sizes contain- 

 ed in the fovilla, of which, in this instance, it appeal's to be 

 entirely composed, and which are seen through its transpa- 

 rent envelope. I could not detect any other bodies but these 

 globules, which I regard as fluid for the reasons just given. 

 The application of iodine to the fovilla, contrary to expecta- 

 tion, produced no effect, and a solution of potash but little 

 apparent results. 



I look forward to another opportunity of making more ex- 

 tended observations upon the nature of these so-called mole- 

 cules. 



Being anxious to ascertain whether stimuli would produce 

 any effect upon the pollen, various solutions were applied 

 with a view to determine this point. The results following 

 the various applications employed were as follows : — solutions 

 of the mineral acids, whether sulphuric, nitric or hydrochloric, 

 all occasioned, with more or less degree of force, the protru- 

 sion of the pollen tubes. Their mode of action is not very 

 clear ; but it may be that they produce some astringent ef- 

 fect upon the outer coating of the pollen grain, so as to cause 

 the princijile of endosmosis to operate with greater power. 

 Sometimes these acids, and more particularly the dilute sul- 

 phuric acid, rupture the inner membrane, and then the 

 fovilla escapes from its interior ; but most frequently the pol- 

 len tubes are emitted, covered by the intine, which remains 

 entire, and it is to explain this protrusion of them that the 

 above explanation is offered. The concentrated sulphuric 

 acid almost always destroys the intine, and frequently also 

 blackens and chars the extine. A solution of the nitric acid, 

 in the proportion of two of the strong acid to three of water, 

 is perhaps the best application for occasioning the emission 

 of the pollen tubes ; but it is as well to have solutions of all 

 the acids of various strengths, for where one fails another will 

 often produce the desired effect. The action of the hydrochlo- 

 ric acid is weaker than that of either of the others. Solutions 

 of (ether and sal volatile produced a marked effect. When 

 either of these were allowed to fall from a glass on the pollen, 

 its granules became distinctly agitated and moved about with 

 considerable velocity, sometimes for the space of two or three 

 minutes. A like effect, but to a much less extent, resulted 

 from the employment of tinctiu'c of cantharides, tincture of 

 capsicum, proof spirit, solution of nitrate of silver in proof 

 si)irit, and essence of ginger, while liquor ammonia; and po- 



