OBSERVATIONS UPON THE POLLEN TUBE. 191 



involving increased turgidity the pores are somewhat more 

 numerous and readily visible. 



On examining living pollen tubes of Narcissus under 

 the microscope the actual extrusion of solid granules 

 through the apex of the tube may be seen. This normally 

 is a very slow and gradual process the granules appearing 

 to work through the wall of the tube and not to pass 

 through a permanent aperture (PI. XI. fig. 10). Only a 

 few particles escape at a time and these form a little clump 

 of finely granular material which remains for a short time 

 adhering to the outer surface of the pollen tube. After 

 the particles have escaped the pore closes up after them 

 and disappears, the walls of the opening fusing together 

 (fig. 11). Changes of turgidity of moderate intensity 

 produced by irrigating the living tubes with concentrated 

 and dilute sugary solutions exercise no immediate effect 

 upon the formation of the pores. 



In some cases a very large and wide terminal opening 

 is formed, which may be from | to § of the diameter of 

 the pollen tube (fig. 12). Through this opening a large 

 part of the contents of the pollen tube escape whilst the 

 water which can now readily enter the pollen tube through 

 the wide terminal opening rapidly disorganizes its con- 

 tents, the granular debris thus formed shewing marked 

 JBrownian movement. 



The opening thus formed differs from a pore only in its 

 much greater size and in its being unable to close when 

 once formed. The same causes which produce the pore 

 also produce by a more violent action these apical ruptures 

 of the pollen tube. The internal turgidity of the pollen 

 tube presses the limiting layer of ectoplasm tightly against 

 the cell wall and the latter stretches until its elastic 

 tension is equalled by the internal hydrostatic pressure. 

 The apex of the pollen tube being softer, more ductile and 



