202 TEANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



plasmic contents thus cut off contains the generative 

 nucleus or nuclei. The formation of these ingrowths is 

 frequently preceded by a general thickening of the wall of 

 the pollen tube ; and is most marked in Vaccinium where 

 the wall may more than double its previous thickness. 



The conditions most favourable for the production of 

 the septa were investigated with pollen of Narcissus by 

 cultivating it in sugary solutions of different strengths. 

 In very dilute solutions the grains become very turgid 

 swelling up considerably. In some cases the limit of 

 stretching being reached the coats burst and the contents 

 escape and become rapidly disorganised but in other cases 

 only the exosporium breaks and the entire endosporium 

 escapes, enlarges considerably and assumes various irregu- 

 lar shapes. Since this enlargement is beyond the limit 

 of stretching growth must have taken place over the 

 entire surface of the endosporium, the irregular shape 

 which the latter assumes being the result of attempts to 

 form a pollen tube, the wall where a protuberance is 

 formed being softer and more ductile than elsewhere. 

 No proper pollen tubes are formed. In a strong sugary 

 solution the grains swell but little and become very 

 transparent. The protoplasm is in most cases shrinks 

 more or less from the wall of the pollen grain and owing 

 to the diminished turgidity of the latter the number and 

 the rapidity of formation of the pollen tubes is much 

 diminished. The shrinking of the protoplasmic contents 

 of the tubes may be so marked, that some of the starch 

 grains are squeezed out of the shrunken protoplasmic 

 mass and lie in the space between it and the wall of the 

 tube. This is especially the case when tubes grown in 

 dilute solutions are placed in concentrated sugary solu- 

 tions. The branching of the pollen tubes, never very 

 abundant, occurs oftenest in strong sugar solutions, and 



