190 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



by which the zymogen particles are extruded, or whether 

 it is a temporary opening made by the particles as they 

 escape, which, being of recent formation, has not yet 

 closed up and disappeared. 



The fact that it is only in relatively few cases that the 

 pore can be seen would seem to indicate that the latter is 

 the more probable view. Supposing, however, that the 

 pore is a permanent structure opening only under the 

 action of an internal pressure caused by a local or general 

 increase of turgidity, the lips of the pore coming so closely 

 together that the latter is obliterated and becomes invisible 

 after turgidity is relieved, then it would only be in a few 

 cases that we should see the pore open and hence visible 

 in a stained and mounted preparation. 



In order to determine whether this latter view was correct 

 or not experiments were performed on pollen tubes by 

 varying their turgidity and then examining them. Pollen 

 tubes of Narcissus which had germinated in a sugar 

 solution of normal strength were placed some in a strong 

 sugar solution and some in a very dilute solution; strong 

 and very dilute solution of potassium nitrate were also 

 used. An hour after, a quantity of a saturated watery 

 solution of picric acid was poured over the pollen tubes 

 in order to kill and fix them in the particular condition in 

 which they might then happen to be. The pollen tubes 

 placed in the dilute solution have their turgidity increased, 

 those in the concentrated solution have their turgidity 

 diminished, hence in the former case if the primary sup- 

 position be true the pores should all be open and visible 

 and in the latter case they should be all closed and 

 invisible. Microscopical examination, however, shews 

 that the pores are no more patent in the former case than 

 in the latter. It was found, however, that after the 

 pollen tubes had been kept for some hours under conditions 



