OBSEBVATIONS UPON THE POLLEN TUBE. 193 



nor does any normal extrusion of grannies appear to take 

 place through such swollen apices. 



When the pollen grain germinates upon the stigma this 

 stage will occur when the apex of the pollen tube reaches 

 the surface of the embryosac and the apical softening 

 which then takes place will readily allow of the extrusion 

 and escape of the male pro-nucleus from the enlarged and 

 swollen apex of the pollen tube. 



To sum up, the reasons for concluding that the minute 

 pore, which may be seen in the apex of certain pollen 

 tubes, is not a permanent structure, but opens on increase 

 and closes on decrease of turgidity, are : 



(1) The pore may be to one side of the apex instead of 

 being terminal, i.e., it does not always occupy the 

 same position. 



(2) More than one pore, as many as two or three, may 

 be present in the apex of one tube. 



(3) After the granules have escaped, the pore totally 

 closes and disappears and may next time be formed 

 in a different situation. 



(4) The bulbous enlargements formed on the ends of 

 the tubes, which are swellings of the softened apex 

 could not be formed if a permanent pore opening on 

 an increase of turgidity taking place were present 

 in the apex of the pollen tube. 



It is worthy of notice as instancing the extreme care 

 needed in interpreting the appearances seen in an investi- 

 gation of this kind that once or twice an appearance was 

 seen in the apex of a pollen tube exactly resembling an oval 

 opening or slit with regular and well marked lips. This 

 was really a depression or crease in the apex of the tube 

 the margins of the depression looking exactly like the lips 

 of an oval slit. Closer examination shews the endos- 

 porium to be continuous between the margins of the 



